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
2.05 2.10 2.15 2.20 2.25 2.30 2.35 2.40 2.453
4
5
6
7
8
9
10
Flux
(10-1
5 erg
cm
-2 s
-1 µ
m-1)
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 Gauss-Hermite 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
2.10 2.15 2.20 2.25 2.30 2.35 2.40-0.2
0.0
0.81.01.21.41.61.82.02.2
Flu
x (1
0-12 e
rg c
m-2 s
-1 µ
m-1)
Wavelength (µm)
2.10 2.15 2.20 2.25 2.30 2.35 2.40
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
Flu
x (1
0-12 e
rg c
m-2 s
-1 µ
m-1)
Wavelength (µm)
Analysis of the stellar kinematics
V* (km s-1)
208
156
104
52 0
-52
-104
-156
-208
σ* (km s-1)
235
247
260
222 209
196
183
171
158
h3
0.16 0.12 0.08 0.04
0.00
-0.04
-0.08 -0.12 -0.16
h4
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
-1.0 -0.5 0.0 0.5 1.0
-200
-100
0
100
200
300
Rad
ial v
eloc
ity
(km
s-1)
Distance to black hole (arcsec)
V* (km s-1)
208
156
104
52 -52 -104
-156 -208
0
-1.0 -0.5 0.0 0.5 1.0140
160
180
200
220
240
260
280
300
Vel
ocit
y di
sper
sion
(km
s-1)
Distance to black hole (arcsec)
σ* (km s-1)
260
247 235
222
209
196
183
171
158
0.16
0.12
0.08
0.04
0.00
-0.04
-0.08
-0.12
-0.16
-1.0 -0.5 0.0 0.5 1.0
-0.2
-0.1
0.0
0.1
0.2
h 3
Distance to black hole (arcsec)
h3
Analysis of the stellar kinematics
Parameter Value M● M�
e
i
ω
σb km s-1
σd km s-1
M/LI
810)0.20.9( ×±
05.012.0 ±
°±° 280
°±° 95
)14260( ±
)8120( ±
5.00.3 ±
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�) 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)
8100.20.9 ×±=•M
Thank you