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