# Detection of a Multi-Phase Ultra-Fast Wind in the
Narrow-Line Seyfert 1 Galaxy Mrk 1044

Y. Krongold Instituto de Astronomía, Universidad Nacional Autónoma de México,
Circuito Exterior, Ciudad Universitaria, Ciudad de México 04510, México  A.L.
Longinotti Instituto de Astronomía, Universidad Nacional Autónoma de México,
Circuito Exterior, Ciudad Universitaria, Ciudad de México 04510, México  M.
Santos-Lleó European Space Agency (ESA), European Space Astronomy Centre
(ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid,
Spain  S. Mathur Department of Astronomy, The Ohio State University, 140 West
18th Avenue, Columbus, OH 43210, USA  Center for Cosmology and Astroparticle
Physics, 191 West Woodruff Avenue, Columbus, OH 43210, USA  B. M. Peterson
Department of Astronomy, The Ohio State University, 140 West 18th Avenue,
Columbus, OH 43210, USA  Center for Cosmology and Astroparticle Physics, 191
West Woodruff Avenue, Columbus, OH 43210, USA  F. Nicastro Observatorio
Astronomico di Roma-INAF, Via di Frascati 33, 1-00040 Monte Porzio Catone, RM,
Italy  A. Gupta Department of Astronomy, The Ohio State University, 140 West
18th Avenue, Columbus, OH 43210, USA  Columbus State Community College, 550 E
Spring St., Columbus, OH 43215, USA  P. Rodríguez-Pascual SERCO for the
European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino
Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain  M. Elías-
Chávez Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis E. Erro
1, Tonantzintla, Puebla, C.P. 72840, Mexico

###### Abstract

We present a detailed analysis of XMM-Newton X-ray spectra of the Narrow-Line
Seyfert 1 galaxy Mrk 1044. We find robust evidence for a multi-phase, ultra-
fast outflow, traced by four separate components in the grating spectrum. One
component has high column density and ionization state, and is outflowing at
$\sim 0.15c$. The other three wind components have lower temperature, lower
column density, and have outflow velocities $\sim 0.08c$. This wind structure
is strikingly similar to that found in IRAS 17020+4544, suggesting that
stratified winds may be a common feature of ultra-fast outflows. Such
structure is likely produced by fluid instabilities that form when the nuclear
wind shocks the ambient medium. We show that in an energy-driven wind
scenario, the wind in Mrk 1044 might carry enough energy to produce
significant feedback on its host galaxy. We further discuss the implications
of the presence of a fast wind in yet another NLS1 galaxy with high Eddington
ratio.

galaxies:Seyfert – quasars:supermassive black holes – X-rays:individual:Mrk
1044

††journal: ApJ††facilities: XMM-Newton††software: SAS (v18.0.0; Gabriel et al.
2004), XSPEC (v12.11; Arnaud 1996), PHASE (Krongold et al. 2003)

##  1 Introduction

Outflows of copious amounts of gas are a common feature observed in many bands
of the electromagnetic spectra of active galactic nuclei (AGNs). The “warm
absorbers” that are observed in the X-ray spectra of about 50% of Seyfert
galaxies provide a detailed view of the ionized gas that is outflowing at
velocities of $10^{2-3}\,\mbox{\rm km\,s${}^{-1}$}$ in the nuclear regions
(Laha et al., 2014, 2021, and references therein).

Much faster winds, the “ultra-fast outflows,” or UFOs, with $v_{\rm
out}>10,000\,\mbox{\rm km\,s${}^{-1}$}$, were initially discovered two decades
ago (e.g. Chartas et al., 2002; Pounds et al., 2003; Reeves et al., 2003;
Dasgupta et al., 2005; O’Brien et al., 2005). Systematic studies of these
systems show a detection fraction in 30–40% of nearby AGNs and indicate they
are likely launched at accretion disk scales, (Tombesi et al., 2010; Gofford
et al., 2013; Tombesi et al., 2013). These winds show mass outflow rates of
around $0.01$–$1M_{\odot}\,{\rm yr}^{-1}$, kinetic energies around
$10^{42-45}\,\mbox{\rm erg\,s${}^{-1}$}$, and are consistent with theoretical
predictions of black hole feedback models (King, 2010).

The effect of AGN winds on the larger-scale environment, commonly referred to
as “AGN feedback,” may have a profound impact on the evolution of the host-
galaxy properties (Di Matteo et al., 2005; Hopkins & Elvis, 2010). Indeed,
quasar feedback is postulated as the mechanism capable of regulating the
relationships between supermassive black holes and their host galaxies that is
required by simulations in order to reproduce the galaxy luminosity function
at high luminosities (see Bower et al., 2006; Kormendy & Ho, 2013). The
discovery of sub-relativistic X-ray winds in very bright quasars (such as PDS
456, Reeves et al., 2003; Nardini et al., 2015) and the relation of the inner
X-ray wind to galaxy-scale outflows (Tombesi et al. 2015, but see revised
estimates of energetics by Veilleux et al. 2017 ; Feruglio et al. 2015;
Longinotti et al. 2018; Mizumoto et al. 2019; Bischetti et al. 2019; Marasco
et al. 2020) supports the role of accretion disk winds as potential feedback
agents. This feedback is expected to play a major role in the early Universe,
during the peaks of star formation and black hole accretion in the Universe.
However, due to the intrinsic difficulty in detecting these systems, only a
few examples of a connection between a sub-pc outflow and a large scale wind
are known at z$>$1 (e.g. Feruglio et al., 2017; Chartas et al., 2020).

Narrow-line Seyfert 1 (NLS1) galaxies constitute a particular sub-class of
AGNs that is defined by an H$\beta$ line width ${\rm FWHM}<2000\,\mbox{\rm
km\,s${}^{-1}$}$ and unusually prominent Fe ii lines (Osterbrock & Pogge,
1985). They are also characterized by extreme X-ray properties (Gallo et al.,
2018) that include strong soft X-ray emission characterized by steep photon
indices, a high degree of continuum variability, and high Eddington ratios.
Recent serendipitous analyses of X-ray grating spectra of NLS1s have shown
that these sources seem to preferentially host UFOs with a very rich
stratified structure (Gupta et al., 2013, 2015; Longinotti et al., 2015;
Parker et al., 2017; Reeves et al., 2018; Reeves & Braito, 2019).

Considering that the archetypical fast wind-quasar PDS 456 (Reeves et al.,
2003; Nardini et al., 2015) also shows a dependence of the wind parameters on
the source luminosity and accretion rate (Matzeu et al., 2017), the occurrence
of ultra-fast outflows seems to be related to phenomena taking place in highly
accreting sources. A straightforward explanation would be that the wind is
launched from the accretion disk via radiatively driven processes (Pinto et
al., 2018). However, recent results suggest that radiative pressure cannot
accelerate UFOs to $\sim$0.1c because when special relativistic effects are
taken into account the absorption cross section of the atoms is greatly
reduced. This implies that the pressure exerted by photons on the fast-
escaping gas particles is also greatly reduced (Luminari et al., 2021). As
such, the exact mechanism behind the launching and acceleration of UFOs
remains a mystery.

Mrk 1044 is a nearby NLS1 at $z=0.016$ with $L_{\rm BOL}=1.4\times
10^{44}\,\mbox{\rm erg\,s${}^{-1}$}$ (Grupe et al., 2010). It is characterized
by a very high Eddington ratio, with reported values ranging from
$\dot{m}\approx 0.59$ (Grupe et al., 2010) to $\dot{m}\approx 16$ (Du et al.,
2015). Mrk 1044 is a barred spiral galaxy, relatively undisturbed (Deo et al.,
2006; Powell et al., 2018) with no signs of interaction (Koulouridis et al.,
2006), and a modest star-formation rate ($L_{\rm FIR}=3\times
10^{9}\,L_{\odot}$; Bertram et al. 2007). It has a small black hole mass
$M_{\rm BH}=2.8\times 10^{6}\,M_{\odot}$, based on reverberation-mapping
measurements (Hu et al. 2015; Du & Wang 2019, though see §6.5). Despite being
one of the X-ray brightest AGN in the local Universe, it has not been
extensively observed by X-ray facilities until relatively recently. Dewangan
et al. (2007) reported on a short XMM–Newton exposure, which highlighted a
strong featureless soft excess and complex temporal behavior. An extensive
analysis of a deeper XMM–Newton observation coupled with NuSTAR and Neil
Gehrels Swift Observatory data (Mallick et al., 2018) concluded that the
excess emission observed in the soft and hard X-ray bands can be explained by
relativistic Compton reflection from a high-density accretion disk. Mallick et
al. (2018) also tentatively reported the presence of a soft X-ray fast
outflow. Comparison with this work is presented in §6.

An intrinsic outflow has been observed in the UV band of Mrk 1044 with a
velocity $v\approx-1150\,\mbox{\rm km\,s${}^{-1}$}$ (Fields et al., 2005a, b)
based on spectra obtained with the Far Ultraviolet Spectroscopic Explorer
(FUSE) and the Hubble Space Telescope (HST). By comparing the O vi, C iv, and
N v column densities with that of H i, they conclude that the metallicity of
the outflow is supersolar.

This paper presents the first detailed spectroscopic analysis of the high
resolution RGS data of Mrk 1044.

##  2 Observations and Data Reduction

XMM–Newton observed Mrk 1044 on 2013 January 27 for a total duration of 133ks
(OBSID 0695290101, PI M. Santos-Lleó). The XMM–Newton EPIC-pn camera was set
to operate in Small Window mode. The data were processed with SAS 18.0.0. The
raw event file was processed with the SAS task EPPROC. Events were
subsequently filtered with PATTERN $\leq$4 (therefore including single and
double events) and FLAG=0. The Good Time Interval (GTI) was created via
standard procedure by filtering the 10-12 keV light curve of the field of view
with a rate of 2 cts s-1 to exclude background flares. Photon pile up was
checked with the EPATPLOT task and found not to be an issue. The net exposure
in the resulting event list is 91 ks.

Source and background spectra were extracted from a circular region of 40 and
53 arc sec radius, respectively, and response matrices were produced with the
SAS tasks RMFGEN and ARFGEN. The source spectrum was rebinned with the task
SPECGROUP to have a minimum number of 25 counts in each spectral channel and
in order to avoid oversampling of the instrumental resolution by a factor
larger than 3. We note that the background in the pn spectrum dominates over
the source spectrum for energies above $\sim$8keV.

The background-subtracted and deadtime-corrected light curve extracted from
the pn counts with the task EPICLCCORR reveals strong variability during the
XMM–Newton observation on timescales of few ks (see Fig. 1). The hardness
ratio, plotted in the bottom panel of Figure 1, indicates that the behavior of
the source flux is similar in the hard and soft bands. As a first-order check
for spectral variability between the flaring and quiescent portions of the
light curve, we assumed a threshold count rate of 17 cts s-1. Consequently,
events were selected above and below this threshold. Spectra extracted from
the “high” and “low” states following the same procedure described above for
the integrated spectrum, do not show any obvious change in the spectral shape.
This can be clearly observed in Figure 2, where the average, high, and low
state spectra are presented against a simple hard-band powerlaw model.

Data obtained by the RGS instrument were processed through the standard
RGSPROC tool and the combined spectrum of RGS1 and RGS2 cameras was obtained
via the standard RGSCOMBINE tool. In addition to the spectrum from the full
exposure of 130 ks, spectra from the “high” and “low” periods were extracted
following the procedure applied to the pn data. RGS spectra were not grouped
during the spectral analysis. The total exposure accumulated by the RGS in the
high and low states is 50 ks and 80 ks, respectively.

Chi-squared statistics was applied when fitting the CCD data and C-statistics
(Cash, 1979) was applied for the grating spectral analysis. A detailed
temporal analysis of the EPIC data was published by Mallick et al. (2018). For
the purpose of this study, we have compared the high and low EPIC and RGS
spectra, applying the same spectral analysis to both of them. We checked for
variations in the properties of the X-ray wind detected in the entire spectrum
(see §3.2). Despite the large flux variations (a factor $\sim$3) we find no
changes in the wind properties between the high and low states. Therefore, we
will discuss only results based on the integrated spectrum from the full
exposure throughout the rest of this paper. In the following, errors are
quoted at the 1$\sigma$ level.

Figure 1: Light curve of Mrk 1044 extracted from the XMM–Newton observation.
From top to bottom: background subtracted source counts in 0.3–2 keV, 2–10 keV
and hardness ratio.  Figure 2: Upper panel: EPIC-pn spectra extracted form the
average, low, and high states of the light curve. The spectra have been
modelled in the 2-10 keV region with a simple powerlaw (solid lines in the
plot). Lower panel: ratio between the data and the hard band powerlaw model.
We do not find strong changes in the spectral shape between the high and low
flux states.

Figure 3:  RGS spectrum in the 8-30 Å range, fitted with a model including a
powerlaw continuum and 16 Gaussians. Main observed/expected absorption lines
by the CGM of our Galaxy at z=0 are marked in magenta. Line identifications
were made by matching this phenomenological fit to the physical model in Table
2. The absorption features coincident with the outflow velocity of UFO1 are
labeled in blue, and those with the velocity of UFO2 are marked in green.
Features consistent with the outflow velocity of UFO3 and UFO4 are shown in
red and black, respectively. The blue dotted line shows the model without the
Gaussians. The spectrum was binned by up to four instrumental channels for
display purposes only. Figure 4: Spectral energy distribution of Mrk 1044 used
to model the ultra-fast outflow wind in this source. Data were obtained from
the NASA Extragalactic Database (black points) and from the XMM–Newton
observation discussed here (red points: Optical Monitor, green line: EPIC-PN
best fit model).

##  3 Spectral Analysis of the High Resolution Data of Mrk 1044

We carried out the analysis of Mrk 1044 RGS data using the unbinned spectrum,
making use of Cash (1979) statistics to perform the spectral fitting in the
software package Xspec (V. 12.11), and subtracting the background spectrum
from the source spectrum.111 According to the Xspec manual, the use of Cash
statistics with a background spectrum with Poisson statistics can produce a
bias in the fit. This is expected only for weak sources and small number of
counts in the background spectrum. Although this is not the case of our
source, we double-checked our fits running them on the data binned by a factor
of 10. We find similar results to those on the unbinned data, confirming that
our results are not affected by this bias.

###  3.1 Modeling the Spectrum with a simple phenomenological model

We started by fitting the continuum in the 8–30 Å (0.4–1.5 keV) range with a
phenomenological model consisting of a powerlaw attenuated by Galactic
absorption, assuming a column density $N_{\rm H}=3.6\times 10^{20}\,\mbox{\rm
cm${}^{-2}$}$ (Willingale et al., 2013), and using the Xspec model TBabs.
Although this is not a physically motivated model, it represents the most
simple description of the continuum to look for the presence of absorption or
emission features. The model gives a reasonable fit to the data, with a $C$
statistic of 2541.5 for 2162 degrees of freedom (d.o.f.). The photon index of
the powerlaw is $\Gamma=2.66\pm 0.01$, typical of the high values obtained in
the soft X-ray band for NLS1s.

Table 1: List of absorption lines individually detected above a 2.5$\sigma$
threshold.

Obs. $\lambda$ | Intensity |  $\Delta$Cstat | Sign. | Line ID | Component
---|---|---|---|---|---
Å |  $10^{-5}$ ph cm-2 s-1 |  | $\sigma$ |  |
8.55${}^{+0.03}_{-0.01}$ | 1.15${}^{+0.12}_{-0.38}$ | 8.0 | 3.0 |  Na xi\+ Ni xxiv | UFO1
9.09$\pm{0.01}$ | 1.72$\pm{0.38}$ | 17.6 | 4.5 | Fe xxiv | UFO1
9.61${}^{+0.01}_{-0.02}$ | 1.30${}^{+0.34}_{-0.30}$ | 15.0 | 4.3 |  Ni xxii\+ Ni xxiii | UFO1
10.36${}^{+0.01}_{-0.03}$ | 0.79$\pm{0.30}$ | 6.1 | 2.6 | Ne x | UFO1
10.94$\pm{0.04}$ | 1.04$\pm{0.41}$ | 5.0 | 2.5 | Fe xxii | UFO2
11.35${}^{+0.03}_{-0.01}$ | 1.33${}^{+0.45}_{-0.38}$ | 9.7 | 3.5 | Fe xx | UFO2
12.50${}^{+0.01}_{-0.05}$ | 1.61$\pm{0.41}$ | 13.6 | 3.9 | Fe xix | UFO2
12.93${}^{+0.04}_{-0.01}$ | 1.12$\pm{0.43}$ | 6.2 | 2.6 |  O viii? | UFO1
17.57${}^{+0.06}_{-0.05}$ | 0.89$\pm{0.35}$ | 5.1 | 2.5 | O viii | UFO2
20.20$\pm{0.01}$ | 1.73$\pm{0.56}$ | 8.1 | 3.1 | O viii | UFO4
26.45$\pm{0.02}$ | 1.79$\pm{0.63}$ | 7.6 | 2.8 | ? | ?
26.64$\pm{0.01}$ | 1.61$\pm{0.61}$ | 6.8 | 2.6 | C vi | UFO4
27.96$\pm{0.03}$ | 2.00$\pm{0.58}$ | 10.3 | 3.4 | N iv | UFO3
28.53$\pm{0.01}$ | 2.05$\pm{0.63}$ | 9.2 | 3.3 | N iii | UFO3
28.81$\pm{0.01}$ | 3.25$\pm{0.65}$ | 20.6 | 5.0 | C vi | UFO1
29.17$\pm{0.01}$ | 2.55$\pm{0.69}$ | 12.4 | 3.7 |  N i? | UFO3

Note. — Identifications were made by matching this phenomenological fit to the
physical model in Table 2

We did not find any evidence of residuals pointing to the presence of emission
features in the spectrum. However, the data show negative residuals throughout
the spectral range, suggestive of absorption lines by ionized gas. We
performed a blind search for individual absorption lines by adding narrow
Gaussian with negative intensity to our simple powerlaw model, over the whole
spectral range. The line widths were fixed to 0.1 eV and their positions and
intensities were left free to vary. All the lines detected above a 2.5$\sigma$
threshold are reported in Table 1. The improvement in C-statistics is measured
for the addition of 2 d.o.f. per line. The significance of the lines was
computed by dividing the intensity of the line over the positive 1$\sigma$
error. Figure 3 presents our phenomenological best fit model consisting of a
simple powerlaw and 16 Gaussians. Several of these features are highly
significant (10 lines have $\sigma\geq$3 and three have $\sigma\geq$4),
showing that the presence of absorbing gas is required by the data. However,
the line positions do not match the common transitions found in warm
absorbers, which typically have outflow velocities up to few thousand
kilometers per second in the rest frame of the source. A clear identification
of the lines was only possible with the aid of physical models to account for
the absorption. Identifications in Figure 3 and Table 1 are based on these
models. The outflow velocity of these absorbers puts them in the range for
UFOs, as we show in the next section.

###  3.2 A Physical model for the UFOs in Mrk 1044

To produce a physical description of the absorption in the RGS spectrum of Mrk
1044, we opted to apply a self-consistent model. For this purpose, we used the
photoionization code PHASE (Krongold et al., 2003), which assumes a slab of
ionized gas in a plane-parallel geometry described by four parameters222A
traditional fifth parameter, the covering factor in the line of sight, was not
considered since the models were consistent with a value of unity.:

  1. 1.

The ionization parameter333The dimensionless ionization parameter is defined
as  $U=\frac{Q}{4\pi R^{2}cn_{e}},$ where $Q$ is the rate at which the source
emits ionizing photons (i.e.. photons per second), $c$ is the speed of light,
and $n_{e}$ and $R$ are the electron density and the distance of the gas from
the X-ray source, respectively.;

  2. 2.

The equivalent hydrogen column density of the slab $N_{\rm H}$;

  3. 3.

The outflow velocity of the wind $v_{\rm out}$; and

  4. 4.

The microturbulence velocity of the medium. Given that the absorption features
in the spectrum are narrow and unresolved, we fix the microturbulence velocity
to $10\,\mbox{\rm km\,s${}^{-1}$}$, however, we note that the exact value
adopted for this parameter has negligible effect on the fit.

Figure 5: RGS spectrum in the 8–30 Å range, fitted with a model including a
powerlaw continuum attenuated by four UFO components. The main absorption
lines produced by UFO1 are labeled in blue, and those by UFO2 are marked in
green. Features by UFO3 and UFO4 are shown in red and black, respectively.
Expected absorption lines by the CGM of our Galaxy at $z=0$ are marked in
magenta. The blue dotted line shows the model without the contribution of
bound-bound absorption. The spectrum was binned by up to four instrumental
channels for display purposes only.

To calculate the ionization balance produced by the impinging ionizing
radiation of the source, we constructed the spectral energy distribution (SED)
for Mrk 1044 using data from the NASA Extragalactic Database and from the
XMM–Newton spectrum discussed here (see Fig. 4).

###  3.3 Evaluating the significance of the UFO components

While fitting the data with the PHASE components, we evaluated the relative
quality of a model including an UFO using two different methods.

First, we used the Akaike Information Criterion values (Akaike, 1974), as done
by Hebbar et al. (2019). These values are defined as444We note that since we
are using the unbinned RGS data, we have a large number of d.o.f. in our
models, and we do not require the correction of the Akaike values for small
sample sizes.:

$AIC=2k+C_{stat}$ (1)

where $k$ is the number of parameters and $C_{stat}$ is the value of the C
statistic for the best fit with a given model. Then, the relative likelihood
that the model including the UFO component is better than the model without it
is given by the quantity exp((AIC(UFO)- AIC(No-UFO))/2). As noted by Hebbar et
al. (2019), the inverse of this quantity represents the factor by which the
more complex model (containing the UFO) is preferred over the simpler model.

The second method to estimate the statistical significance of the UFO
components consisted in running Monte Carlo simulations. To do this, we
followed the procedure in Longinotti et al. (2015, hereafter L15). As a
baseline model for these simulations, we employed the phenomenological
continuum model described in §3.1 (consisting in a powerlaw with Galactic
absorption). We include any previous UFO component already in the model, as
done in the actual spectral fitting (see §3.4). For example, we included in
the simulations only the continuum model to test the significance of one UFO,
we included continuum+UFO1 for testing the significance of the second UFO,
etc. For each UFO component, we produced 1000 synthetic spectra with the XSPEC
package, each with the same photon statistics as the real data set. Following
L15, we recorded the improvement in $C$-statistics by adding a new PHASE
component to the baseline model. The final distribution of $\Delta C_{sim}$ in
the simulations was then fit assuming a Gaussian profile. 555The actual
distribution of $\Delta C_{sim}$ does not follow an exact Gaussian profile,
but assuming such a profile represents a very conservative way to estimate the
significance of the fitted components.. The significance of each UFO component
was calculated by dividing the $\Delta C_{Stat}$ of the best fit model in the
real data, over the 1$\sigma$ range of the Gaussian model to the distribution
of $\Delta C_{sim}$ in the simulations.

###  3.4 Results to the fit of the RGS data with the PHASE components

We started by including one PHASE component to our model, thus we fit the data
with a powerlaw attenuated by a slab of photoionized gas (with the ionization
parameter, the column density, and the outflow velocity of the absorber free
to vary), and further attenuated by the gas in our Galaxy. This model provides
a large improvement to the fit, with $\Delta C=81/3$ d.o.f. (the C-statistic
of the fit with a simple powerlaw was 2541.5 for 2162 d.o.f.), pointing to the
presence of a highly significant absorber in the line of sight (see below). We
note that this absorber (hereafter UFO1) has a very large outflow velocity,
$v_{\rm out}\approx 0.15c$ (see Table 2). Thus, in addition to its high column
density ($N_{\rm H}\approx 10^{23}\,\mbox{\rm cm${}^{-2}$}$), the absorption
lines are strongly shifted to the blue with respect to the rest frame of Mrk
1044, explaining why identification of these features was not possible by
simple visual inspection of the spectrum. The ionization state of UFO1 is also
quite high ($\log U\approx 2.2$), producing absorption by ions such as C vi, N
vii, O viii, Ne x, and Fe xxii–Fe xxiv, among others, but not high enough to
produce Fe xxv–Fe xxvi, as observed in other UFOs (e.g., Parker et al., 2018).
The significance of UFO1 was evaluated as described in §3.3. It turned out to
be much greater than $10\sigma$, using Monte Carlo simulations. The comparison
of AIC statistics (Table 2) also indicates a very large significance: The
model including UFO1 is preferred by a factor of 2$\times 10^{16}$ over the
model considering only the continuum.

Table 2: Best fit parameters of the phenomenological continuum and the
multiphase ultra-fast wind detected in the RGS spectrum of Mrk 1044. Single
Powerlaw Continuum Parameters
---
$\Gamma$ |  | Norm.($10^{-3}$ ph keV cm-2 s-1) |  | AIC |  |
$2.82\pm 0.01$ |  | $8.0\pm 0.1$ |  | 2545.5 |  |
Wind Parameters
Wind Phase | $\log U$ | $\log N_{\rm H}$ | $v_{\rm out}$ | Statistics | AIC | Factor | Significance
- |  | (cm-2) | (km s-1) |  $\Delta C$/$\Delta\nu$ |  |  |
UFO1 | $2.2\pm 0.1$ | $22.9_{-0.1}^{+0.2}$ | $44800_{-70}^{+130}$ | 81/3 | 2470.5 | 2$\times 10^{16}$ | $>>10\sigma$
UFO2 | $1.6\pm 0.1$ | $21.2_{-0.024}^{+0.25}$ | $26084_{-240}^{+90}$ | 21/3 | 2455.5 | 1808 | $4\sigma$
UFO3 | $-2.7\pm 0.1$ | $20.6\pm 0.1$ | $23670_{-270}^{+180}$ | 36/3 | 2425.5 | 3$\times 10^{6}$ | $6\sigma$
UFO4 | $-0.2\pm 0.1$ | $20.3\pm 0.1$ | $23430_{-110}^{+190}$ | 17/3 | 2414.5 | 245 | $3\sigma$
Final Statistic
Cstat/$\nu$ 2386.5/2150

Although the presence of UFO1 accounts for a large part of the residuals to a
powerlaw in the spectrum, strong residuals remain (including the Gaussian fits
not identified with this UFO, see Fig. 3). Therefore, we continued fitting the
data by iteratively adding additional PHASE components to the model (as we did
with UFO1, for each component, the ionization parameter, column density, and
outflow velocity were free parameters). Three more statistically significant
PHASE components (see below), each with $\Delta C>15$ for the three new free
parameters, were required. This components are hereafter designated UFO2,
UFO3, and UFO4. Table 2 presents the results of our best fit, including the
continuum and four UFO components. Figure 5 compares the best fit with the
spectrum.

Statistical significances for UFO2, UFO3, and UFO4 were evaluated as described
in §3.3. Using Monte Carlo simulations, they are $\sim 4\sigma$ for UFO2,
$\sim 6\sigma$ for UFO3, and $\sim 3\sigma$ for UFO4. AIC statistics
comparison indicates that UFO2, UFO3 and UFO4 improve the fit by factors
$\approx$ 1800, 3$\times 10^{6}$, and 250, respectively (see Table 2).

The new UFO components have roughly half the speed of UFO1 ($v\approx 0.08c$),
and at least 50 times lower column density. UFO2 is highly ionized and
absorption by O viii and Fe xix–Fe xii is detected (green labels in Fig. 5).
On the other hand, UFO3 has very low ionization, with dominant ions O i–O iv
and N ii–N iv (red labels in Fig. 5). Finally UFO4 has an intermediate level
of ionization, with features due to O vii–O viii and N vi–N vii. It is
noteworthy that UFO3 and UFO4 have strikingly similar velocities, fully
consistent within the errors, pointing to a common origin for these two
components.

Our final fit still leaves some residuals, particularly near 26.45 and 29.17Å
(see Table 1), where Gaussians with significance 2.8 and 3.7$\sigma$ were
required. The line at 29.17Å is consistent with absorption by N i at the same
velocity of UFO3, however this component does not have enough neutral material
to produce this feature. This indicate that the structure of this UFO
component might be more complex than the simple absorbing slab model presented
here. The feature at 26.45Å cannot be accounted for with the addition of a
further significant UFO component or with the presence of a Galactic line at
z=0, and thus, it remains unidentified in our analysis.

##  4 Analysis of the Low-Resolution EPIC-pn data

Motivated by our results on the wind found with the RGS data, we modelled the
EPIC-pn data with two goals in mind. First, we wanted to test the presence of
the UFO components found in the RGS data. Second, we wanted to search for
higher-ionization absorption by Fe xxv and Fe xxvi that might coexist with the
presence of UFO1, whose ionization range extends up to Fe xxiv.

Mallick et al. (2018) found that the broad-band spectrum of Mrk 1044 can be
well described by a model consisting of relativistic reflection from a high-
density accretion disk with a broken powerlaw emissivity profile. Given that
this model represents a physically motivated description of the continuum, we
follow their analysis. The EPIC-pn data were modelled with a primary continuum
component represented by a simple powerlaw, a relativistically blurred
reflection component to account for the accretion disk reflection (modelled
with the high-density model RELXILLD; García et al. 2016), and a distant
reflector to account for the narrow FeK$\alpha$ emission line (XILLVERD model;
García et al. 2016). All these components were further attenuated by Galactic
absorption.

A description of the parameters for the XILLVERD and RELXILLD models is
presented in Table 3. We set the spectral index of these components to be the
same as that of the direct continuum. The RELXILLD model was included in the
fit with the rest of its parameters free, with the exception of the outer
radius of the disk, which was fixed to 1000rg (where rg =
GM${\rm{}_{BH}/c^{2}}$). For the XILLVERD component, we fix the ionization
parameter to 0, assuming neutral gas for the distant reflector. We also fixed
the density to $10^{15}$ cm-3 (the lowest value allowed by the model), and the
inclination angle to 60o. In this way, the broad-band continuum was fit with
14 free parameters, two of the primary continuum source, 10 of the
relativistic reflector and two of the distant reflector (Table 3).

As in Mallick et al. (2018), we ignored the spectral range between 1.8-2.5 keV
because of the instrumental edges produced by Si at 1.8 keV and Au at 2.2 keV
(e.g. Marinucci et al., 2014; Matt et al., 2014). This model provides a
relatively good representation of the data, with $\chi^{2}=1059.5$ for 947
d.o.f. The residuals to this fit are preseneted in the middle panel of Figure
6.

Table 3: Best-fit parameters for the physically motivated continuum and the
multiphase ultra-fast wind detected in the EPIC-pn spectrum of Mrk 1044.
Primary Continuum Source
---
$\Gamma$ | $2.39\pm 0.01$ | Photon index
Npc ($10^{-3}$ ph keV cm-2 s-1) | $4.6\pm 0.3$ | Normalisation
Relativistic Reflection (RELXILLD)
qin | $8.17\pm 0.24$ | Inner emissivity index
qout | $1.72^{+0.34}_{-0.25}$ | Inner emissivity index
Rbr (rg) | $6.5^{+3.5}_{-0.3}$ | Break disk radius
a | $0.994^{+0.002}_{-0.008}$ | SMBH spin
$\theta^{o}$ | $46.5^{+1.8}_{-7.3}$ | disk inclination angle
Rin (rg) | $1.26^{+.34}_{-0.04}$ | Inner disk radius
Rout (rg) (fixed) | $1000$ | Outer disk radius
$\Gamma$ (tied to primary continuum) | $2.39$ | Blurred reflection photon index
log($\xi$) [erg cm s-1] | $3.06^{+.03}_{-0.07}$ | Ionization parameter of the disk
AbFe | $1.3^{+.5}_{-0.1}$ | Iron abundance (solar)
log(ne) [cm-3] | $15.2^{+.2}_{-0.1}$ | Electron density of the disk
Nblur ($10^{-4}$) | $2.4^{+0.3}_{-0.2}$ | Normalisation of the relativistic reflector
Distant Reflection (XILLVERD)
$\Gamma$ (tied to primary continuum) | $2.39$ | Distant reflection photon index
AbFe | $0.61^{+.12}_{-0.07}$ | Iron abundance (solar)
log(ne) [cm-3] (fixed) | $15.0$ | Electron density of the distant reflector
log($\xi$) [erg cm s-1] (fixed) | 0 | Ionization parameter of the distant reflector
$\theta^{o}$ (fixed) | 60 | Inclination angle of the distant reflector
Ndist ($10^{-4}$) | $0.77^{+0.08}_{-0.07}$ | Normalisation of the distant reflector
Wind Parameters UFO 1
log(U) | $2.4\pm 0.1$ | Ionization parameter
log(NH) [cm-2] | $23.3^{+0.1}_{-0.2}$ | Columns Density
Vout (fixed) (km s-1) | 44790 | Outflow Velocity
$\Delta$ $\chi^{2}$/$\Delta$$\nu$ | 41.9/2 | Improvement including UFO 1
Wind Parameters UFO 3
log(U) | $-2.9\pm 0.1$ | Ionization parameter
log(NH) [cm-2] | $20.2^{+0.1}_{-0.2}$ | Columns Density
Vout (fixed) (km s-1) | 23610 | Outflow Velocity
$\Delta$ $\chi^{2}$/$\Delta$$\nu$ | 19.1/2 | Improvement including UFO 3
Final Statistic
$\chi^{2}$/$\nu$ | 998.5/943 | Final statistic
Figure 6: Model and residuals between the EPIC-pn spectrum and the model
discussed in §4 in the 0.3–10 keV range. Top panel: Data and best fit model.
Middle panel: Residuals to a continuum model consisting of a primary continuum
source plus relativistic and distant reflection. Lower panel: Residuals to the
best fit model including continuum reflection components plus two UFO
components. The residuals are plotted in units of the standard deviation.

We then added the different UFO components found in the RGS analysis to this
baseline model to test their presence. We left free to vary the ionization
parameter and column density of each PHASE component. However, we fixed the
outflow velocity to the best fit value obtained in our final model of the RGS
data, which will be presented in §5 (our final description of the RGS data
consists of the same, physically motivated continuum model presented here,
including relativistic and distant reflection, plus the UFO components). We
note that in these models, the distant reflection component (XILLVERD) was not
attenuated by the ionized wind, as it should lie further out.

We find that UFO2 and UFO4 are not required by the EPIC-pn data as adding them
to the model results in only a marginal decrease in $\chi^{2}$. However, UFO1
and UFO3 are clearly required in the fit. The improvement in the statistics
after including UFO1 is $\Delta\chi^{2}=41.9$ for a difference of 2 d.o.f. The
improvement by UFO3 is $\Delta\chi^{2}=19.1$/2 d.o.f.

Table 3 shows the parameters of our best-fit model, that is presented in
Figure 6. The UFO parameters are fully consistent with those found over the
phenomenological model of the RGS data (see Table 2), with the exception of
the column density of UFO1, who is $\sim$2 times higher in the CCD model. This
result will be further discussed in §5. The presence of UFO1 is required due
to its high opacity produced by bound-bound transitions. On the other hand,
UFO3 is required by the fit because of its bound-free opacity above 1 keV.
Finally, we note that the continuum parameters are similar those obtained by
Mallick et al. (2018).

The EPIC-pn data do not show evidence of UFO absorption by higher ionization
species such as Fe xxv or Fe xxvi. There are no strong residuals between 7.6
and 8 keV, where absorption features by Fe xxv or Fe xxvi are expected for gas
outflowing at the velocity of UFO1 (see Fig. 6). This is consistent with the
ionization state of UFO1, that predicts no absorption by these charge states.
We do not find strong evidence of absorption at other velocities either.

##  5 Modelling the RGS high resolution data with a physically motivated model

The continuum in the high RGS data of Mrk 1044 was well described with a
phenomenological model with a powerlaw (§3.1). However, the analysis over the
EPIC-pn data showed far more complexity than this simple model, including
relativistic reflection by the disk. In this section, we model the RGS data of
Mrk 1044 including a physically motivated model for both the UFO and the
continuum.

We start by applying the same continuum model applied to the low resolution
data. The model consists of a direct emission source (powerlaw) plus
relativistic (RELXILLD) and distant reflection (XILLVERD), attenuated by
Galactic absorption. We note, however, that the RGS covers only a fraction of
the overall spectral range of the EPIC-pn. Then, some of the parameters of the
model cannot be well constrained with the RGS alone. To circumvent this
problem, we fixed as many parameters as possible in the RGS model to their
best fit values on the low resolution data. We find that the RGS can be well
fit by a model with only seven free parameters: The spectral index and
normalization of the powerlaw, the emissivity index for the outer and inner
portions of the disk, as well as the disk break radius and normalization for
the RELXILLD component, and finally the normalization for the XILLVERD
component. The spectral index of both reflection components was fixed to the
same value of the powerlaw component. The rest of the parameters were
constrained to the values reported in Table 3 (a model with these parameters
free does not give physically meaningful results, and does not improve
significantly the fit). This model gives a $C$ statistic of 2475 for 2157
d.o.f.

Table 4: Best fit parameters of the physically motivated continuum and the
multiphase ultra-fast wind detected in the RGS spectrum of Mrk 1044. Primary
Continuum Parameters
---
$\Gamma$ | Norm. ($10^{-3}$ ph keV cm-2 s-1) |  |  | AIC |  |
$2.57\pm 0.07$ | $6.0\pm 0.6$ |  |  |  | 2489 |  |
Relativistic Reflection Parameters∗
$\Gamma$ | Norm. ($10^{-4}$) |  $q_{in}$∗∗ |  $q_{out}$∗∗ | Rbr∗∗ (rg) |  |  |
$2.57$(fixed) | $1.1\pm 0.2$ | $7.36\pm 0.45$ | $2.87_{-0.44}^{+0.23}$ | $12.9^{+1.5}_{-4.4}$ |  |  |
Distant Reflection Parameters∗
$\Gamma$ | Norm. ($10^{-4}$) |  |  |  |  |  |
$2.57$(fixed) | $0.06\pm 0.04$ |  |  |  |  |  |
Wind Parameters
Wind Phase | $\log U$ | $\log N_{\rm H}$ | $v_{\rm out}$ | Statistics | AIC | Factor | Significance
- |  | (cm-2) | (km s-1) |  $\Delta C$/$\Delta\nu$ |  |  |
UFO1 | $2.3\pm 0.1$ | $23.2_{-0.1}^{+0.2}$ | $44790_{-60}^{+140}$ | 37/3 | 2458 | 5$\times 10^{6}$ | $8\sigma$
UFO2 | $1.8\pm 0.1$ | $21.2_{-0.12}^{+0.19}$ | $25960_{-230}^{+140}$ | 19/3 | 2445 | 665 | $4\sigma$
UFO3 | $-3.1\pm 0.2$ | $20.3\pm 0.1$ | $23610_{-250}^{+210}$ | 20/3 | 2431 | 1096 | $4\sigma$
UFO4 | $-0.1\pm 0.1$ | $20.2\pm 0.1$ | $23420_{-120}^{+190}$ | 16/3 | 2421 | 148 | $3\sigma$
Final Statistic
|  | Cstat/$\nu$ | 2383/2145 |  |  |  |

We then proceed to include in the modelling the four UFO components in the
same order that were found in §3.4. As before, we quantitatively evaluated the
improvement of each component to the fit with the aid of the Akaike
Information Criterion values, and with Monte Carlo simulations as described in
§3.3. We found that the four UFO components are required to fit the data. UFO1
is required at an 8$\sigma$ level with the Monte Carlo methods. The AIC
statistics indicate that the model including this component is 5$\times
10^{6}$ times better than the model without it. Although these numbers are
smaller than those found with the phenomenological model, this UFO has a very
high significance. Monte Carlo simulations show that UFO2, UFO3 and UFO4 are
required with significance 4$\sigma$, 4$\sigma$, and 3$\sigma$, respectively.
AIC statistics show that the model with UFO2 is better by a factor
$\approx$650, the one with UFO3 is better by a factor $\approx$1100 and the
model including UFO4 by a factor $\approx$150.

Table 4 presents the results of our best fit. The continuum parameters are
similar, yet not equal, than those found in the EPIC-pn data. This is likely
because of the much larger sensibility of the high-resolution data to detect
individual narrow absorption lines, which results in this model requiring the
presence of UFO2 and UFO4.

It is noteworthy that the best fit values obtained for the wind components are
strikingly similar to those obtained with the phenomenological model of the
continuum presented in §3.4. This shows that the UFO properties are basically
defined by the presence of the absorption lines. The only exception to this is
the column density of UFO1. As was the case for the EPIC-pn data, the value of
the column density was twice that found with a simple powerlaw. We note that
this physically motivated continuum model requires a slightly higher continuum
in the 6-12Å band (both over the high and low resolution data), where most of
the bound-bound opacity of this UFO is present. Thus, the larger column
density in this component is required to balance the larger continuum, and fit
well the depth of the absorption lines. Nevertheless, the final fit cannot be
easily differentiated by eye to the one presented in Figure 5.

In the following, we discuss our results with the model presented in this
section, that includes a physically reasonable description of the continuum
and absorption components.

##  6 Discussion

###  6.1 Comparison with Previous Studies

The present analysis confirms the results of Mallick et al. (2018) indicating
that the broad-band spectra of Mrk 1044 (including the soft excess) can be
well explained by a model consisting of relativistic blurred reflection of the
primary continuum source by a high-density accretion disk that has a broken
powerlaw emissivity profile.

We note that Mallick et al. (2018) also report the presence of a UFO, with
column density of 4.7$\times 10^{20}$ cm-2, an outflow velocity of 0.1c, and
high ionization state. However, the UFO reported by these authors is
remarkably different than the UFO components presented here in that it is
detected as a very broad absorption profile ($\sigma\sim$15,000 km -1),
associated with an O viii feature near 0.7 keV. This absorption feature is
found in the EPIC-pn and RGS data after extrapolating the continuum model in
the 3-10 keV region to the whole band.

Our models of the data do not require this broad feature (in neither the low
and high resolution data). We find that our continuum modelling for EPIC-pn
predicts only a modest broad absorption feature near 0.7 keV (see middle panel
of Fig. 6). Our final fit, including two UFOs, can account for the most part
of the spectral broad-band shape, including the absorption near this energy
region (as seen in the lower panel of Fig. 6). Figures 3 and 5 show the same
for the RGS.

We have also found that the depth and width of this broad line-like structure
depends on the exact continuum parameters of the relativistic reflection
component, and that this feature is not required with a different description
of the whole band continuum (i.e., a model consisting of a powerlaw with a
distant neutral reflector plus a “traditional” soft excess modelled by two
blackbodies or by an additional powerlaw).

The evidence for the reality of the UFO components reported here is based upon
the simultaneous detection of several statistically significant narrow
absorption lines. These absorption lines can be fit simultaneously with
physically motivated self-consistent absorption models, whose properties are
basically independent of the continuum modelling.

With this in mind, we consider the UFO description presented here a more
reliable representation of the data. We note that the main purpose of the
analysis presented by Mallick et al. (2018) was to understand the physical
processes behind the continuum emission, while our analysis is centered in
understanding the absorbing systems.

###  6.2 Ultrafast Outflows and Narrow Line Seyfert 1 Nuclei

Mrk 1044 represents another case of an NLS1 in which a UFO has been detected.
Over the years, there has been an increasing number of subrelativistic winds
in this type of AGN. Other detections include Akn 564 (Gupta et al., 2013),
IRAS 17020+4544 (L15), PG 1211+143 (Reeves et al., 2018), 1H 0707-495 (Kosec
et al., 2018), 1 Zw 1 (Reeves & Braito, 2019), and IRAS 13224$-$3809 (Parker
et al., 2017). This might not result entirely surprising, since one of the
prevailing ideas for the launching mechanism of these winds is that they are
radiatively driven (Matzeu et al., 2017) and NLS1 galaxies have suitably high
Eddington ratios. We note, however, that recent results cast doubts on the
efficiency of radiation to accelerate gas to subrelativistic speeds (up to
0.1c, Luminari et al., 2021). In any case, the large fraction of UFOs detected
in NLS1 points to an intimate dependence of the UFO launching mechanism,
whatever it might be, with the accretion rate.

###  6.3 Multi-Phase UFOs in AGN

Mrk 1044 shows a complex ultra-fast outflow wind structure consisting of four
different absorbing components: a “heavy” and very hot absorber with roughly
twice the velocity of the other three slower and much lighter components (the
“light” components). There is a vast range of column densities, differing by
up to a factor of $\sim 1000$, and ionization states, differing in $U$ by
nearly five orders of magnitude, between the hottest and coolest components in
the overall outflow. It is noteworthy that, within the errors, two of the
light absorbers (UFO3 and UFO4) have the same velocity and the same column
density, within a factor of two. This is suggestive of a single system
spanning a vast range of temperatures, or a multi-phase outflow.

This overall structure is not unprecedented. L15 reported a multi-phase UFO in
IRAS 17020+4544, with a single component dominating the mass and dynamics,
plus four lighter components. Strong differences in ionization state and
column density among the components were also found in that case. L15 also
found two different UFOs with the same outflow velocity. In comparison, the
wind in IRAS 17020+4544 has half the velocity of that found in Mrk 1044. In
that case, all the components have similar velocities, including the “heavy”
component. In both objects, the lines are narrow and unresolved, pointing to
negligible acceleration along the line of sight. Gupta et al. (2013, 2015)
also found evidence of multi-phase UFOs in Ark 564 and Mrk 590. Recently,
Parker et al. (2020) observed a multi-phase outflow in IRAS 13349+2438, with
two highly ionized components absorbing in the Fe K band, and a lower
ionization Ly$\alpha$ line accompanying the slower component. A few other
examples of multiple-ionization UFOs exist, including PDS 456 (Reeves et al.,
2018) and MCG-03-58-007 (Braito et al., 2018; Matzeu et al., 2019).

The similar characteristics of the UFOs in these objects, particularly Mrk
1044 and IRAS 17020+4544, introduce a new view of UFOs. They show much more
complex structure than a simple wind produced by one or two lines of highly
ionized Fe. These results also show that lower ionization UFOs exist, contrary
to the expectations of models where the wind is bound to exist only at higher
ionization levels (e.g., King, 2010). The CCD and grating data on Mrk 1044
exclude the presence of such highly ionized material (no Fe xxv or Fe xxvi
absorption is detected), and show that the nature of UFO1 is the same as that
of the UFOs detected in the Fe K band of other objects with similar column
densities and velocities, but with significantly lower ionization. The “heavy
component” of L15 (UFO C in their paper) may represent an even more extreme
case of this.

###  6.4 The Nature of the Different Wind Phases

The multi-phase structure of these outflows offers valuable clues to
understanding their nature. A simple scenario where dense blobs of lower
ionization material are embedded in a larger scale wind (the “heavy” absorber)
is ruled out by the UFOs detected in Mrk 1044, as the difference in velocity
among the components, nearly $0.1c$, would produce shear forces that would
destroy the blobs on very short timescales. Yet, in some cases, these
components persist over timescales of years, e.g., component A in IRAS
17020+4544 (L15).

In the few cases with multi-phase outflows detected in the Fe K band — IRAS
13349+2438 (Parker et al., 2020), PDS 456 (Reeves et al., 2020), and
MCG-03-58-007 (Matzeu et al., 2019) — the presence of different components can
be explained by a disk wind with different streamlines crossing our line of
sight to the central engine, with the more ionized and faster material coming
from smaller radii (e.g., Fukumura et al., 2015). In these sources, the
different velocity components detected in absorption all have high column
densities ($N_{\rm H}\approx 10^{23-24}$ cm-2), and the column densities of
the lower ionization material can vary by two orders of magnitude (Reeves et
al., 2020).

The striking resemblance of the UFOs in Mrk 1044 and IRAS 17020+4544, and
their difference with respect to the Fe K band multi-phase UFOs, suggests that
in this case the mechanism might be different. Given the low ionization states
and column densities of the “light” components in these objects, different
streamlines crossing our line of sight are unlikely. Such light and warm/cold
components arising directly from the accretion disk are difficult to explain,
and their subrelativistic velocities would make them highly unstable.

The properties of the phases in these two objects might instead be more easily
understood in terms of a “shocked outflow” scenario. This model posits an
initial fast outflow, launched at accretion disk scales with outflow velocity
$\sim 0.1c$ that shocks the ambient medium (see King & Pounds, 2015). In such
a scenario, fluid instabilities (e.g., Rayleigh–Taylor) may form at the
interface of the shock, as occurs in supernova remnants (Velazquez et al.,
1998) due to the difference between the densities of the impacting wind and
the impacted medium. A condition for the Rayleigh–Taylor instability to grow
is that the mass of the ISM that is pushed by the discontinuity should be
higher than the mass of the ejecta (Velazquez et al., 1998), which undergoes a
deceleration process that is able to trigger instabilities in the fluid. A
hydrodynamic toy model simulating the formation of such instabilities within
the central region of a NLS1 is presented by Longinotti (2020), including
typical UFO parameters. The results show that “plumes” or “fingers” of gas
with velocities of the same order of magnitude as the incident UFO are formed
as a result of instability processes in the expansion of the shocked outflow.
When these “fingers” intercept our line of sight to the center, they can
produce the “light” UFO components observed in the spectra (see also Sanfrutos
et al., 2018). Furthermore, entrained colder material would naturally explain
the presence of the very low ionization states found in UFO3, and its common
speed with UFO4. Thus the overall structure of these winds might be explained
by this scenario.

###  6.5 Implications for Feedback

It is now well established, at least using simple energetic arguments, that
UFOs carry enough power to quench star formation in their hosts and influence
the evolution of galaxies. According to Hopkins & Elvis (2010), a wind
transferring energy outwards in an energy-driven mode requires a minimum power
to produce feedback $\sim 0.5$% of the Eddington luminosity.666 In an “energy-
driven” wind scenario, most of the energy of the UFO is transferred outwards
and injected into the insterstellar medium, rather than radiated away As we
show below, the UFO in Mrk 1044 is not an exception, and may satisfy this
condition.

We first address the question of the black hole mass. Du & Wang (2019) give a
mass of $M=2.85\times 10^{6}\,\mbox{$M_{\odot}$}$ based on reverberation
measurements (Hu et al., 2015). Unfortunately, the only line-width measurement
quoted is FWHM(H$\beta$), which introduces a bias by stretching the mass
scale, i.e., low masses are underestimated and high masses are overestimated
(Dalla Bontà et al., 2020). However, it is possible to remove this bias
empirically. We take from Du & Wang (2019) the luminosity of the H$\beta$ line
and adjust it to the cosmological parameters used by Dalla Bontà et al.
(2020), i.e., $H_{0}=72$ km s-1 Mpc-1, $\Omega_{\Lambda}=0.7$, $\Omega_{\rm
m}=0.3$, which gives $\log L(\mbox{\rm H$\beta$})=41.33\pm 0.09$, where
$L(\mbox{\rm H$\beta$})$ is in ergs per second. Taking the line width ${\rm
FWHM}=1178\pm 22$ km s-1from Du & Wang (2019) and using equations (40) and
(41) of Dalla Bontà et al. (2020) gives $M=3.78\,(\pm 1.45)\times
10^{6}\,\mbox{$M_{\odot}$}$. The corresponding Eddington luminosity is $L_{\rm
Edd}=1.26\times 10^{38}(M/\mbox{$M_{\odot}$})=4.76\times 10^{44}$ erg s-1.

To estimate the energetics of the outflow in Mrk 1044, we assume that the
outflow velocity is larger than or equal to the escape velocity at the launch
radius. We take this to be $r=2GM/v_{\rm out}^{2}$ Under this condition, the
mass outflow rate for a radial wind in spherical geometry crossing our line of
sight can be estimated by

$\dot{M}_{\rm out}=4\pi\mu m_{p}rN_{\rm H}v_{\rm out}C_{f},$ (2)

where $m_{p}$ and $\mu$ correspond to the mass of the proton and to the mean
atomic mass per particle ($\mu=1.4$), $C_{f}$ to the covering fraction of the
outflow, and $N_{\rm H}$ and $v_{\rm out}$ to the column density and the
observed velocity of the outflow, respectively (Tombesi et al., 2015).
Following L15, we can express this formula in units of 1021 cm-2 ($N_{\rm
H}=N_{21}\times 10^{21}\,{\rm cm}^{-2}$) and $10,000\,\mbox{\rm
km\,s${}^{-1}$}$ ($v_{\rm out}=v_{10}\times 10^{4}\,\mbox{\rm
km\,s${}^{-1}$}$) as

$\displaystyle\dot{M}_{\rm out}$ $\displaystyle=$ $\displaystyle 7.80\times
10^{15}\left(\frac{M}{M_{\odot}}\right)\left(\frac{N_{21}}{v_{10}}\right)C_{f}\,{\rm
g\,s}^{-1}$ (3) $\displaystyle=$ $\displaystyle 1.24\times
10^{-10}\left(\frac{M}{M_{\odot}}\right)\left(\frac{N_{21}}{v_{10}}\right)C_{f}M_{\odot}\,{\rm
yr}^{-1}.$

The energy outflow rate, or kinetic luminosity, is

$\dot{E}=\frac{1}{2}\dot{M}_{\rm out}v_{\rm out}^{2}\\\ =3.9\times
10^{33}\left(\frac{M}{\mbox{$M_{\odot}$}}\right)\ N_{21}\ v_{10}\ C_{f}\
\mbox{\rm erg\,s${}^{-1}$}.$

We find that UFO1 is the only component that could produce feedback. Using
$N_{\rm H}$ and $v_{\rm out}$ from Table 4 yields

$\dot{M}_{\rm out}\approx 1.6\times 10^{-2}C_{f}\
{\rm\mbox{$M_{\odot}$}\,yr}^{-1},$ (4)

and

$\dot{E}=1.0\times 10^{43}\ C_{f}\ \mbox{\rm erg\,s${}^{-1}$}.$ (5)

The Hopkins & Elvis (2010) criterion for triggering feedback by an energy-
conserving wind is

$\frac{\dot{E}}{L_{\rm Edd}}=0.02C_{f}>0.005,$ (6)

which is satisfied for $C_{f}>0.25$. We note that this value bares caveats
associated with the location of the wind that goes in the estimation of
$\dot{E}$, and with the black hole mass which goes in the estimation of
$L_{\rm Edd}$, as discussed above. Thus, the above ratio should be taken with
care.

The studies of Tombesi et al. (2010) and Gofford et al. (2013) found that the
fraction of Seyfert galaxies with UFOs is about 30-40%. If this fraction is
interpreted as a proxy for the global covering factor of the wind, the UFO in
Mrk 1044 would meet the theoretical feedback condition for a wind in the
energy-conserving mode. Although these are estimates based on strong
assumptions, an emerging picture seems to be arising where winds in NLSy1
might be capable of strong feedback.

On the other hand, if most of the thermal energy released at the shock front
of the UFO with the interstellar medium is radiated away, the wind in Mrk 1044
would not have a major transforming effect on its host galaxy, as the
criterion for feedback in the “momentum-conserving” regime is much more
demanding: ${\dot{E}}/{L_{\rm Edd}}~{}>~{}0.1$.

We note, however, that even if the wind falls short to produce strong feedback
and completely halt star formation, it could still have important effects on
the host galaxy. For instance, if the wind could expand above and below the
disk (directions of least resistance), it could inflate bubbles in the
circumgalactic medium of the galaxy on timescales of millions of years,
similar to the so-called Fermi bubbles in the Milky Way (Faucher-Giguère &
Quataert 2012; see Nicastro et al. 2016 for further details). However, we note
that if this were the case, the feedback is only in its very early stages, as
no evidence for such bubbles is found in the analysis of MUSE optical data of
Mrk 1044 (Powell et al., 2018). An early stage in the feedback process is also
suggested by the lack of X-ray warm absorbers in Mrk 1044, because the
“outflow shock model” predicts the formation of these systems as the shocked
gas cools down and slows down.

The UFOs in IRAS 17020+4544 and Mrk 1044 show that feedback is not exclusive
to the most luminous active galaxies in the Universe (e.g., Chartas et al.,
2002; Tombesi et al., 2015; Nardini et al., 2015), but can take place even in
Seyferts with moderate luminosity.

##  7 Conclusions

Mrk 1044 provides evidence for a bona-fide ultra-fast outflow in the soft
X-ray spectrum of an NLS1 galaxy. The increasing number of UFOs detected in
NLS1s suggests an intimate relation between the high accretion rates in this
type of AGN, and the mechanism responisble for the launching of the winds. The
nature of the outflow in Mrk 1044, with a multi-velocity, multi-phase
structure, is strikingly similar to that found in IRAS 17020+4544. It appears
that the structure of subrelativistic outflows is more complex than thought
before. The presence of a “heavy” hot component supports the idea of a
“shocked outflow” where the lighter and warmer absorbing components form by
instabilities in the shock. The energetics of the wind could be sufficient to
produce strong feedback effects on the host galaxy in the so-called “energy-
conserving mode”, showing (along with IRAS 17020+4544) that such feedback
might not be exclusive of the most luminous active galaxies in the Universe,
but can take place even in Seyfert galaxies of moderate luminosity.

We thank the anonymous referee for his/her useful comments. YK acknowledges
support from DGAPA-UNAM grant IN106518, DGAPA-PASPA 2016-2017 and from the
Faculty of the European Space Astronomy Centre (ESAC). ALL acknowledges
support from CONACyT grant CB-2016-286316.

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