HST emission-line images of nearby 3CR radio galaxies: two photoionization, accretion and feedback modes

We present HST/ACS narrow-band images of a low-z sample of 19 3C radio galaxies to study the H$\alpha$ and [OIII] emissions from the narrow-line region (NLR). Based on nuclear emission line ratios, we divide the sample into High and Low Excitation Galaxies (HEGs and LEGs). We observe different line morphologies, extended line emission on kpc scale, large [OIII]/H$\alpha$ scatter across the galaxies, and a radio-line alignment. In general, HEGs show more prominent emission line properties than LEGs: larger, more disturbed, more luminous, and more massive regions of ionized gas with slightly larger covering factors. We find evidence of correlations between line luminosities and (radio and X-ray) nuclear luminosities. All these results point to a main common origin, the active nucleus, which ionize the surrounding gas. However, the contribution of additional photoionization mechanism (jet shocks and star formation) are needed to account for the different line properties of the two classes. A relationship between the accretion, photoionization and feedback modes emerges from this study. For LEGs (hot-gas accretors), the synchrotron emission from the jet represents the main source of ionizing photons. The lack of cold gas and star formation in their hosts accounts for the moderate ionized-gas masses and sizes. For HEGs (cold-gas accretors), an ionizing continuum from a standard disk and shocks from the powerful jets are the main sources of photoionization, with the contribution from star formation. These components, combined with the large reservoir of cold/dust gas brought from a recent merger, account for the properties of their extended emission-line regions.Comment: accepted for publication on ApJ (22 pages, 12 figures

VLT-VIMOS integral field spectroscopy of luminous and ultraluminous infrared galaxies: III. the atlas of the stellar and ionized gas distribution

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 C2 kpc parameter, which measures the concentration of the emission within the central 2 kpc. The C2 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 C2 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 star-formation 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. © 2011 ESO.Based on observations carried out at the European Southern observatory, Paranal (Chile), Programs 076.B- 0479(A), 078.B-0072(A) and 081.B-0108(A).The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166.This work has been supported by the Spanish Ministry of Science and Innovation (MICINN) under grant ESP2007-65475-C02-01. AM-I is supported by the Spanish Ministry of Science and Innovation (MICINN) under program “Specialization in International Organisms”, Ref. ES2006-0003.Peer Reviewe

Higher prevalence of X-ray selected AGN in intermediate age galaxies up to z~1

We analyse the stellar populations in the host galaxies of 53 X-ray selected optically dull active galactic nuclei (AGN) at 0.34<z<1.07 with ultra-deep (m=26.5) optical medium-band (R~50) photometry from the Survey for High-z Absorption Red and Dead Sources (SHARDS). The spectral resolution of SHARDS allows us to consistently measure the strength of the 4000 AA break, Dn(4000), a reliable age indicator for stellar populations. We confirm that most X-ray selected moderate-luminosity AGN (L_X<10^44 erg/s) are hosted by massive galaxies (typically M*>10^10.5 M_sun) and that the observed fraction of galaxies hosting an AGN increases with the stellar mass. A careful selection of random control samples of inactive galaxies allows us to remove the stellar mass and redshift dependencies of the AGN fraction to explore trends with several stellar age indicators. We find no significant differences in the distribution of the rest-frame U-V colour for AGN hosts and inactive galaxies, in agreement with previous results. However, we find significantly shallower 4000 AA breaks in AGN hosts, indicative of younger stellar populations. With the help of a model-independent determination of the extinction, we obtain extinction-corrected U-V colours and light-weighted average stellar ages. We find that AGN hosts have younger stellar populations and higher extinction compared to inactive galaxies with the same stellar mass and at the same redshift. We find a highly significant excess of AGN hosts with Dn(4000)~1.4 and light weighted average stellar ages of 300-500 Myr, as well as a deficit of AGN in intrinsic red galaxies. We interpret failure in recognising these trends in previous studies as a consequence of the balancing effect in observed colours of the age-extinction degeneracy.Comment: Accepted for publication in MNRAS, 12 pages, 8 figures, 1 tabl

Integral field spectroscopy based Hα sizes of local luminous and ultraluminous infrared galaxies. A direct comparison with high-z massive star-forming galaxies

[Aims]: We study the analogy between local luminous and ultraluminous infrared galaxies (U/LIRGs) and high-z massive star forming galaxies (SFGs) by comparing their basic Hα structural characteristics, such as size and luminosity surface density, in an homogeneous way (i.e. same tracer, size definition, and similar physical scales). [Methods]: We use integral field spectroscopy (IFS) based Hα emission maps for a representative sample of 54 local U/LIRGs (66 galaxies) observed with INTEGRAL/WHT and VIMOS/VLT. From this initial sample, we select 26 objects with similar Hα luminosities (L(Hα)) to those of massive (i.e. M * ∼ 10 10 M ⊙ or larger) SFGs at z ∼ 2, and observed on similar physical scales. We then directly compare the sizes, and luminosity (and SFR) surface densities of these local and high-z samples. [Results]: The size of the Hα emitting region in the local U/LIRGs that we study has a wide range of values, with r 1/2(Hα) from 0.2 kpc to 7 kpc. However, about two-thirds of local U/LIRGs with L ir > 10 11.4 L ⊙ have compact Hα emission (i.e. r 1/2 2 kpc). These are systems that show evidence of pre-coalescence merger activity and are indistinguishable from the massive high-z SFGs galaxies in terms of their Hα sizes, and luminosity and SFR surface densities. © 2012 ESO.MGM is supported by the German federal department for education and research (BMBF) under the project number 50OS1101. This work has been supported by the Spanish Ministry of Science and Innovation (MICINN) under grants ESP2007-65475- C02-01 and AYA2010-21161-C02-01.Peer Reviewe

Starburst radio galaxies: General properties, evolutionary histories and triggering

In this paper we discuss the results of a programme of spectral synthesis modelling of a sample of starburst radio galaxies in the context of scenarios for the triggering of the activity and the evolution of the host galaxies. New optical spectra are also presented for a subset of the objects discussed. The starburst radio galaxies - comprising ∼15-25 per cent of all powerful extragalactic radio sources - frequently show disturbed morphologies at optical wavelengths, and unusual radio structures, although their stellar masses are typical of radio galaxies as a class. In terms of the characteristic ages of their young stellar populations (YSPs), the objects can be divided into two groups: those with YSP ages tYSP≤ 0.1 Gyr, in which the radio source has been triggered quasi-simultaneously with the main starburst episode, and those with older YSP in which the radio source has been triggered or re-triggered a significant period after the starburst episode. Most of the former group are associated with a large mid- to far-IR (MFIR) continuum and [Oiii] emission-line luminosities (LIR > 1011L⊙, W), while most of the latter have lower luminosities. Combining the information on the YSP with that on the optical morphologies of the host galaxies, we deduce that the majority of the starburst radio galaxies have been triggered in galaxy mergers in which at least one of the galaxies is gas rich. However, the triggering (or re-triggering) of the radio jets can occur immediately before, around or a significant period after the final coalescence of the merging nuclei, reflecting the complex gas infall histories of the merger events. Although ∼25 per cent of starburst radio galaxies are sufficiently bright at MFIR wavelengths to be classified as ultraluminous infrared galaxies (ULIRGs), we show that only the most massive ULIRGs are capable of evolving into radio galaxies. Finally, for a small subset of starburst radio galaxies in rich clusters of galaxies, cooling flows associated with the hot X-ray haloes offer a viable alternative to mergers as a trigger for the radio jet activity. Overall, our results provide further evidence that a powerful radio jet activity can be triggered via a variety of mechanisms, including different evolutionary stages of major galaxy mergers; clearly, radio-loud AGN activity is not solely associated with a particular stage of a unique type of gas accretion event. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.This research has made use of the NASA/IPAC Extragalactic Data base (NED) which is operated by the Jet Propulsion Laboratory. Based on observations made with ESO Telescopes at the La Silla and Paranal observatories under programmes 70.B-0663(A), 71.B-0320(A), 078B-0660(A).Peer Reviewe

Shards: An optical spectro-photometric survey of distant galaxies

Pérez-González et al.We present the Survey for High-z Absorption Red and Dead Sources (SHARDS), an ESO/GTC Large Program carried out using the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias (GTC). SHARDS is an ultra-deep optical spectro-photometric survey of the GOODS-N field covering 130 arcmin2 at wavelengths between 500 and 950 nm with 24 contiguous medium-band filters (providing a spectral resolution R ∿ 50). The data reach an AB magnitude of 26.5 (at least at a 3σ level) with sub-arcsec seeing in all bands. SHARDS' main goal is to obtain accurate physical properties of intermediate- and high-z galaxies using well-sampled optical spectral energy distributions (SEDs) with sufficient spectral resolution to measure absorption and emission features, whose analysis will provide reliable stellar population and active galactic nucleus (AGN) parameters. Among the different populations of high-z galaxies, SHARDS' principal targets are massive quiescent galaxies at z > 1, whose existence is one of the major challenges facing current hierarchical models of galaxy formation. In this paper, we outline the observational strategy and include a detailed discussion of the special reduction and calibration procedures which should be applied to the GTC/OSIRIS data. An assessment of the SHARDS data quality is also performed. We present science demonstration results on the detection and study of emission-line galaxies (star-forming objects and AGNs) at z = 0-5. We also analyze the SEDs for a sample of 27 quiescent massive galaxies with spectroscopic redshifts in the range 1.0 < z ≲ 1.4. We discuss the improvements introduced by the SHARDS data set in the analysis of their star formation history and stellar properties. We discuss the systematics arising from the use of different stellar population libraries, typical in this kind of study. Averaging the results from the different libraries, we find that the UV-to-MIR SEDs of the massive quiescent galaxies at z = 1.0-1.4 are well described by an exponentially decaying star formation history with scale Ï„ = 100-200 Myr, age around 1.5-2.0 Gyr, solar or slightly sub-solar metallicity, and moderate extinction, A(V) ∿ 0.5 mag. We also find that galaxies with masses above M* are typically older than lighter galaxies, as expected in a downsizing scenario of galaxy formation. This trend is, however, model dependent, i.e., it is significantly more evident in the results obtained with some stellar population synthesis libraries, and almost absent in others. © 2013. The American Astronomical Society. All rights reserved.We acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2009-07723-E and AYA2009-10368. SHARDS has been funded by the Spanish MICINN/MINECO under the Consolider-Ingenio 2010 Program grant CSD2006-00070: First Science with the GTC. O.G.-M., C.M.-T., J.M.R.-E., and J.R.-Z. wish to acknowledge support from grant AYA2010-21887-C04-04. A.A.-H. and A.H.-C. acknowledge financial support from the Universidad de Cantabria through the Augusto G. Linares Program.Peer Reviewe

Stellar Populations in local LIRGs and ULIRGs

Trabajo presentado en el Space Telescope Science Institute (STScI), celebrado en Baltimore (Estados Unidos) del 2 al 5 de mayo de 201

Higher prevalence of X-ray selected AGN in intermediate-age galaxies up to z ~ 1

et al.We analyse the stellar populations in the host galaxies of 53 X-ray selected optically dull active galactic nuclei (AGN) at 0.34 1010.5 M⊙) and that the observed fraction of galaxies hosting an AGN increases with the stellar mass. A careful selection of random control samples of inactive galaxies allows us to remove the stellar mass and redshift dependences of the AGN fraction to explore trends with several stellar age indicators. We find no significant differences in the distribution of the rest-frame U - V colour for AGN hosts and inactive galaxies, in agreement with previous results. However, we find significantly shallower 4000Å breaks in AGN hosts, indicative of younger stellar populations.With the help of a model-independent determination of the extinction, we obtain extinction-corrected U - V colours and light-weighted average stellar ages. We find that AGN hosts have younger stellar populations and higher extinction compared to inactive galaxies with the same stellar mass and at the same redshift. We find a highly significant excess of AGN hosts with Dn(4000) ~ 1.4 and light-weighted average stellar ages of 300-500 Myr, as well as a deficit of AGN in intrinsic red galaxies. We interpret failure in recognizing these trends in previous studies as a consequence of the balancing effect in observed colours of the age-extinction degeneracy. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.AH-C and AA-H acknowledge funding by the Universidad de Cantabria Augusto González Linares programme and the Spanish Plan Nacional de Astronomía y Astrofísica under grant AYA2012-31447. PE and PGP-G acknowledge support from the Spanish Plan Nacional grant AYA2012-31277.Peer Reviewe

PMAS Optical Integral Field Spectroscopy of Luminous Infrared Galaxies

Trabajo presentado en el Workshop Extreme Starbursts in the Local Universe, celebrado en el Instituto de Astrofísica de Andalucía en Granada (España), del 21 al 25 de junio de 201