Tuesday 06/12/2012

Herschel observations of a z~2 stellar mass selected galaxy sample drawn from the GOODS NICMOS Survey

Authors: M. Hilton, C. J. Conselice, I. G. Roseboom, D. Burgarella, V. Buat, S. Berta, M. Béthermin, J. Bock, S. C. Chapman, D. L. Clements, A. Conley, L. Conversi, A. Cooray, D. Farrah, E. Ibar, G. Magdis, B. Magnelli, G. Marsden, R. Nordon, S. J. Oliver, M. J. Page, P. Popesso, F. Pozzi, B. Schulz, Douglas Scott, A. J. Smith, M. Symeonidis, I. Valtchanov, M. Viero, L. Wang, M. Zemcov
(Submitted on 11 Jun 2012)

Abstract: We present a study of the far-IR properties of a stellar mass selected sample of 1.5 < z < 3 galaxies with log(M_*/M_sun) > 9.5 drawn from the GOODS NICMOS Survey (GNS), the deepest H-band Hubble Space Telescope survey of its type prior to the installation of WFC3. We use far-IR and sub-mm data from the PACS and SPIRE instruments on-board Herschel, taken from the PACS Evolutionary Probe (PEP) and Herschel Multi-Tiered Extragalactic Survey (HerMES) key projects respectively. We find a total of 22 GNS galaxies, with median log(M_*/M_sun) = 10.8 and z = 2.0, associated with 250 um sources detected with SNR > 3. We derive mean total IR luminosity log L_IR (L_sun) = 12.36 +/- 0.05 and corresponding star formation rate SFR_(IR+UV) = (280 +/- 40) M_sun/yr for these objects, and find them to have mean dust temperature T_dust ~ 35 K. We find that the SFR derived from the far-IR photometry combined with UV-based estimates of unobscured SFR for these galaxies is on average more than a factor of 2 higher than the SFR derived from extinction corrected UV emission alone, although we note that the IR-based estimate is subject to substantial Malmquist bias. To mitigate the effect of this bias and extend our study to fainter fluxes, we perform a stacking analysis to measure the mean SFR in bins of stellar mass. We obtain detections at the 2-4 sigma level at SPIRE wavelengths for samples with log(M_*/M_sun) > 10. In contrast to the Herschel detected GNS galaxies, we find that estimates of SFR_(IR+UV) for the stacked samples are comparable to those derived from extinction corrected UV emission, although the uncertainties are large. We find evidence for an increasing fraction of dust obscured star formation with stellar mass, finding SFR_IR/SFR_UV \propto M_*^{0.7 +/- 0.2}, which is likely a consequence of the mass–metallicity relation.

Comments: Accepted for publication in MNRAS, 17 pages, 17 figures
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1206.2319v1 [astro-ph.CO]

The ionized gas in the central region of NGC 5253: 2D mapping of the physical and chemical properties

Authors: Ana Monreal-Ibero (1), Jeremy R. Walsh (2), Jose M. Vilchez (1), ((1) Instituto de Astrofisica de Andalucia (CSIC), (2) European Southern Observatory)
(Submitted on 11 Jun 2012)

Abstract: ABRIDGED: NGC5253 was previously studied by our group with the aim to elucidate in detail the starburst interaction processes. Some open issues regarding the 2D structure of the main properties of the ionized gas remain to be addressed. Using IFS data obtained with FLAMES, we derived 2D maps for different tracers of electron density (n_e), electron temperature (T_e) and ionization degree. The maps for n_e as traced by several line ratios are compatible with a 3D stratified view of the nebula with the highest n_e in the innermost layers and a decrease of n_e outwards. To our knowledge, this is the first time that a T_e map based on [SII] lines for an extragalactic object is presented. The joint interpretation of our two T_e maps is consistent with a T_e structure in 3D with higher temperatures close to the main ionizing source surrounded by a colder and more diffuse component. The highest ionization degree is found at the peak of emission for the gas with relatively high ionization in the main GHIIR and lower ionization degree delineating the more extended diffuse component. Abundances for O, Ne and Ar are constant over the mapped area within <0.1 dex. The mean 12+log(O/H) is 8.26 while the relative abundances of log(N/O), log(Ne/O) and log(Ar/O) were \sim-1.32, -0.65 and -2.33, respectively. There are two locations with enhanced N/O. The first (log(N/O)\sim-0.95) is associated to two super star clusters. The second (log(N/O)\sim-1.17), reported here for the first time, is associated to two moderately massive (2-4×10^4 M_sun) and relatively old (\sim10 Myr) clusters. A comparison of the N/O map with those produced by strong line methods supports the use of N2O2 over N2S2 in the search for chemical inhomogeneities within a galaxy. The results on the localized nitrogen enhancement were used to compile and discuss the factors that affect the complex relationship between Wolf-Rayet stars and N/O excess.

Comments: 16 pages, 14 figures, accepted for publication in A&A
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1206.2275v1 [astro-ph.CO]
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