The molecular H2 emission and the
stellar kinematics in the nuclear
region of the Sombrero galaxy
Roberto Bertoldo Menezes
and
J. E. Steiner
Instituto de Astronomia, Geofísica e Ciências Atmosféricas
Universidade de São Paulo
Introduction
•  M104 is an SA(s)a galaxy at a distance of 9.2 Mpc
•  Based on it optical nuclear emission-line spectrum, this object has been
classified as a Low Ionization Nuclear Emission-line Region (LINER –
Heckman 1980)
•  Kormendy (1988), using CFHT data, Emsellem et al. (1994), using
axisymmetric Jeans models and CFHT data, and Kormendy et al. (1996), using
HST and higher resolution CFHT data, obtained a mass of 109 M€ for the SBH
•  Magorrian et al. (1998), using axisymmetric Jeans models, HST and ground
based data, determined a mass of (6.47+0.08-0.19) x 108 M€ for the SBH
•  Using HST, GNIRS and SAURON data, Jardel et al. (2011) applied the
Schwarzschild model and obtained a mass of (6.6 ±0.4) x 108 M€ for the SBH
This work
•  In this work, we analyze a data cube of the nuclear region of M104, observed
with NIFS
•  Our goals are:
- to analyze the infrared emission-line spectrum
- to analyze the stellar kinematics
- to obtain na estimate for the mass of the SBH
Observations, reduction and data treatment
•  The observations of M104 were taken with the Near-Infrared Integral Field
Spectrograph (NIFS), in the K band, with a central wavelength of 2.2 µm
•  The data reduction was made with the Gemini IRAF package
•  After the data reduction, a data treatment procedure (Menezes et al. 2014,
2015), including the following steps, was applied to all data cubes:
- correction of the differential atmospheric refraction
- calculation of a median of the data cubes
- spatial re-sampling of the data cubes, in order to obtain spaxels of 0.021”
- Butterworth spatial filtering
- Richardson-Lucy deconvolution (Richardson 1972; Lucy 1974)
•  The PSF of the final data cube has a FWHM of ~0.15”
Observations, reduction and data treatment
9
8
7
6
Flux (10
-15
-2
-1
-1
erg cm s µm )
10
5
4
3
2.05 2.10 2.15 2.20 2.25 2.30 2.35 2.40 2.45
Wavelength (µm)
Analysis of the emission line spectrum
•  In order to perform an accurate starlight subtraction, we applied the Penalized
Pixel Fitting (pPXF) method (Cappellari & Emsellem 2004) to all the spectra of
the data cube
•  This method uses a combination of template spectra, convolved with a GaussHermite expansion, to fit the observed stellar spectrum
•  This procedure also provides the values of: the stellar radial velocity (V*), the
stellar velocity dispersion (σ*), and the Gauss-Hermite coefficients h3 and h4
•  We used a base of stellar spectra, observed with NIFS, described by Winge et
al. (2009)
•  The obtained synthetic stellar spectra were subtracted from the observed ones,
resulting in a data cube with emission lines only
Analysis of the emission line spectrum
0.08
2.2
0.06
-1
erg cm s µm )
1.8
-2
1.2
-12
1.0
Flux (10
-2
-12
Flux (10
1.4
0.8
0.0
-0.2
0.04
-1
1.6
-1
-1
erg cm s µm )
2.0
2.10
2.15
2.20
2.25
2.30
Wavelength (µm)
2.35
2.40
0.02
0.00
-0.02
-0.04
2.10
2.15
2.20
2.25
2.30
Wavelength (µm)
2.35
2.40
Analysis of the stellar kinematics
σ* (km s-1)
V* (km s-1)
208
156
104
52
0
-52
-104
-156
-208
0.08
222
209
196
183
171
158
h4
0.16
235
247
h3
260
0.12
0.04
0.00
-0.04
-0.08
-0.12
-0.16
0.14
0.10
0.07
0.03
0.00
-0.03
-0.07
-0.10
-0.14
Analysis of the stellar kinematics
•  We simulated a thin eccentric stellar disk around the nucleus
•  126 concentric elliptic orbits were superposed, taking as free parameters ω,
M●, i, and e
•  The stellar mass was determined using and HST image, obtained with WFPC2
in the I band. The mass-to-light ratio (M/LI) was taken as another free parameter
•  The stellar velocity dispersions of the disk (σd) and of the bulge (σb) were also
taken as free parameters
Analysis of the stellar kinematics
V* (km s-1)
300
208
0
-156 -208 -0.5
0.0
0.5
Distance to black hole (arcsec)
1.0
σ* (km s-1)
260
280
-1
247 260
222
220
209
200
196
183
180
171
160
140
235
240
158
-1.0
-0.5
0.0
0.5
Distance to black hole (arcsec)
1.0
h3
0.2
0.16
0.12
0.1
h3
0.08
0.04
0.0
0.00
-0.1
-0.2
-104
300
-52 -100
0
-1.0
Velocity dispersion (km s )
52 -200
104
100
156
-1
Radial velocity (km s )
200
-0.04
-0.08
-0.12
-0.16
-1.0
-0.5
0.0
0.5
Distance to black hole (arcsec)
1.0
Analysis of the stellar kinematics
Parameter
M●
Value
(9.0 ± 2.0) ×108 M€
e
0.12 ± 0.05
i
80° ± 2°
ω
5° ± 9°
σb
(260 ± 14) km s-1
σd
(120 ± 8) km s-1
M/LI
3.0 ± 0.5
Conclusions
•  The image and the RGB composite image of the H2 λ21218 emission line
indicate that the molecular gas is disposed along a rotating torus/disk structure
•  The maps of V*, σ*, and h3 obtained with the pPXF method revealed the
existence of a “cold” rotating stellar disk superposed to a “hot” stellar bulge
•  The dynamical modelling of a thin eccentric disk reproduced the main
properties of the V* and σ* maps, specially within a distance of 0.2” from the
kinematic axis
•  The value of the mass of the SBH we obtained ( M • = 9.0 ± 2.0 ×108 M€) is
compatible, at 1σ or 2σ levels, with the estimates found by many previous
studies (Kormendy 1988; Emsellem et al. 1994; Kormendy et al. 1996;
Magorrian et al. 1998; Jardel et al. 2011)
Thank you