VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies

Abstract

Context. Luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) are much more numerous at higher redshifts than locally, dominating the star-formation rate density at redshifts ∼1-2. Therefore, they are important objects in order to understand how galaxies form and evolve through cosmic time. Local samples provide a unique opportunity to study these objects in detail. Aims. We aim to characterize the morphologies of the stellar continuum and the ionized gas (Hα) emissions from local sources, and investigate how they relate with the dynamical status and IR-luminosity of the sources. Methods. We use optical (5250-7450 Å) integral field spectroscopic (IFS) data for a representative sample of 38 sources (31 LIRGs and 7 ULIRGs), taken with the VIMOS instrument on the VLT. Results. We present an atlas of IFS images of continuum emission, Hα emission, and Hα equivalent widths for the sample. The morphologies of the Hα emission are substantially different from those of the stellar continuum. The Hα images frequently reveal extended structures that are not visible in the continuum, such as HII regions in spiral arms, tidal tails, rings, bridges, of up to few kpc from the nuclear regions. The morphologies of the continuum and Hα images are studied on the basis of the C 2 kpc parameter, which measures the concentration of the emission within the central 2 kpc. The C 2 kpc values found for the Hα images are higher than those of the continuum for the majority (85%) of the objects in our sample. On the other hand, most of the objects in our sample (∼62%) have more than half of their Hα emission outside the central 2 kpc. No clear trends are found between the values of C 2 kpc and the IR-luminosity of the sources. On the other hand, our results suggest that the star formation in advance mergers and early-stage interactions is more concentrated than in isolated objects. Finally, we compared the Hα and infrared emissions as tracers of the starformation activity. We find that the star-formation rates derived using the Hα luminosities generally underpredict those derived using the IR luminosities, even after accounting for reddening effects.

The X-ray emission of local luminous infrared galaxies

“…The star-formation in local LIRGs is distributed over few kpc scales Hattori et al 2004;Rodríguez-Zaurín et al 2011). This is similar to local starbursts and z ∼ 2 infrared bright galaxies (Daddi et al 2007;Rigby et al 2008;Farrah et al 2008;Rujopakarn et al 2010), but at odds with local ULIRGs where most of the activity is taking place in very compact regions (the central kpc).…”

Star-formation laws in luminous infrared galaxies

“…The remaining five LIRGs were selected to populate the high end of the IR luminosity distribution of LIRGs. For the AlonsoHerrero et al LIRGs we obtained HST/NICMOS Paα imaging (Alonso-Herrero et al 2001, 2002, as well as groundbased optical integral field spectroscopy using CAHA/PMAS and VLT/VIMOS covering the Hα spectral region (AlonsoHerrero et al 2009;Rodríguez Zaurín et al 2011). In addition there are MIR Spitzer imaging observations for the entire sample from the GOALS sample (Armus et al 2009).…”

“…This was shown by recent integral field spectroscopy studies of a sample of more than 50 LIRGs and ULIRGs Rodríguez-Zaurín et al 2011). Therefore no corrections were applied to derive the SFR surface density for LIRGs and ULIRGs.…”

Integral field spectroscopy based Hαsizes of local luminous and ultraluminous infrared galaxies

“…The VIMOS sample is presented in Rodríguez-Zaurín et al (2011) and is drawn from the IRAS Revised Bright Galaxy Sample (Sanders et al 2003), the IRAS 1 Jy sample of ULIRGs (Kim et al 1998), and the HST/WFPC2 snapshot sample of bright ULIRGs (ID 6346 PI: K.Borne). These are mainly southern objects.…”

“…We use integral field spectroscopy (IFS) based Hα emission maps obtained from our INTEGRAL/WHT (William Herschel Telescope) and VIMOS/VLT (Very Large Telescope) observations to derive these properties for a representative sample of local U/LIRGs (e.g. Colina et al 2005;García-Marín et al 2009a;Rodríguez-Zaurín et al 2011, and references therein). We compare our results with those for high-redshift massive SFGs samples observed with near-infrared IFS on similar linear scales, using the same tracer (e.g.…”