Wednesday 17th Oct 2012


Molecular gas in the centre of nearby galaxies from VLT/SINFONI integral field spectroscopy – I. Morphology and mass inventory

Authors: X. Mazzalay (1), R. P. Saglia (1 and 2), Peter Erwin (1), M. H. Fabricius (1 and 2), S. P. Rusli (1 and 2), J. Thomas (1 and 2), R. Bender (1 and 2), M. Opitsch (1), N. Nowak (3), Michael J. Williams (1)

We present the first results of an analysis of the properties of the molecular gas in the nuclear regions (r < 300 pc) of a sample of six nearby galaxies, based on new high spatial resolution observations obtained in the K-band with the near-infrared integral field spectrograph SINFONI at the Very Large Telescope. We derive two-dimensional distributions of the warm molecular and ionized gas from the H2, Br_gamma and HeI emission lines present in the spectra of the galaxies. We find a range of morphologies, including bar- and ring-like distributions and either centrally peaked or off-centre emission. The morphologies of the molecular and the ionized gas are not necessarily coincident. The observed emission-line ratios point towards thermal processes as the principal mechanism responsible for the H2 excitation in the nuclear and circumnuclear regions of the galaxies, independently of the presence of an active nucleus. We find that a rescaling of the H2 2.12 microns emission-line luminosity by a factor beta~1200 gives a good estimate (within a factor of 2) of the total (cold) molecular gas mass. The galaxies of the sample contain large quantities of molecular gas in their centres, with total masses in the ~ 105 – 108 Msol range. Never the less, these masses correspond to less than 3 per cent of the stellar masses derived for the galaxies in these regions, indicating that the presence of gas should not affect black hole mass estimates based on the dynamical modelling of the stars. The high-spatial resolution provided by the SINFONI data allowed us to resolve a circumnuclear ring (with a radius of ~270 pc) in the galaxy NGC 4536. The measured values of the Br_gamma equivalent width and the HeI/Br_gamma emission-line ratio suggests that bursts of star formation occurred throughout this ring as recently as 6.5 Myr ago.

arXiv:1210.4316 A cold gas reservoir to fuel M31 nuclear black hole and stellar cluster

Authors: A.-L. Melchior, F. Combes

With IRAM-30m/HERA, we have detected CO(2-1) gas complexes within 30 arcsec (~100 pc) from the center of M31 amounting to a minimum total mass of 4.2 x 10^4 Msol (one third of the positions are detected). Averaging the whole HERA field, we have shown that there is no additional undetected diffuse component. We show that the above gas detection is associated with gas lying on the far side as no extinction is observed in the optical, but some emission is present on infra-red Spitzer maps. The kinematics is complex. (1) The velocity pattern is mainly redshifted: the dynamical center of the gas differs from the black hole position and the maximum of optical emission, and only the red-shifted side is seen in our data. (2) Several velocity components are detected in some lines of sight.
Our interpretation is supported by the reanalysis of the effect of dust on a complete planetary nebula sample. Two dust components are detected with respective position angles of 37 deg and -66 deg. This is compatible with the superposition of the (PA=37 deg) disk dominated by the 10-kpc ring and the inner 0.7-kpc ring detected in infrared data, which position angle (-66 deg) can be measured for the first time. The large scale disk, which dominates the HI data, is very inclined (i=77 deg), warped and superposed on the line of sight on the less inclined inner ring. The detected CO emission might come from both components.


Spectral Energy Distributions of low-luminosity radio galaxies at z~1-3: a high-z view of the host/AGN connection

Authors: Ranieri D. Baldi (1,2), Marco Chiaberge (2,3,4), Alessandro Capetti (5), Javier Rodriguez-Zaurin (2,6), Susana Deustua (2), William B. Sparks (2),

We study the Spectral Energy Distributions, SEDs, (from FUV to MIR bands) of the first sizeable sample of 34 low-luminosity radio galaxies at high redshifts, selected in the COSMOS field. To model the SEDs we use two different template-fitting techniques: i) the Hyperz code that only considers single stellar templates and ii) our own developed technique 2SPD that also includes the contribution from a young stellar population and dust emission. The resulting photometric redshifts range from z ~0.7 to 3 and are in substantial agreement with measurements from earlier work, but significantly more accurate. The SED of most objects is consistent with a dominant contribution from an old stellar population with an age ~1 – 3 10^{9} years. The inferred total stellar mass range is ~10^{10} – 10^{12} M(sun). Dust emission is needed to account for the 24micron emission in 15 objects. Estimates of the dust luminosity yield values in the range L_{dust} ~10^{43.5} -10^{45.5} erg s^{-1}. The global dust temperature, crudely estimated for the sources with a MIR excess, is ~ 300-850 K. A UV excess is often observed with a luminosity in the range ~ 10^{42}-10^{44} erg s^{-1} at 2000 A rest frame.
Our results show that the hosts of these high-z low-luminosity radio sources are old massive galaxies, similarly to the local FRIs. However, the UV and MIR excesses indicate the possible significant contribution from star formation and/or nuclear activity in such bands, not seen in low-z FRIs. Our sources display a wide variety of properties: from possible quasars at the highest luminosities, to low-luminosity old galaxies.

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