arXiv subjects

T. Diaz-Santos

Publications and source records attributed to T. Diaz-Santos.

65 records · Page 4Linked to original sources

arXiv2011

A mid-IR study of Hickson Compact Groups II. Multi-wavelength analysis of the complete GALEX-Spitzer Sample

We present a comprehensive study on the impact of the environment of compact galaxy groups on the evolution of their members using a multi-wavelength analysis, from the UV to the infrared, for a sample of 32 Hickson compact groups (HCGs) containing 135 galaxies. Fitting the SEDs of all galaxies with the state-of-the-art model of da Cunha (2008) we can accurately calculate their mass, SFR, and extinction, as well as estimate their infrared luminosity and dust content. We compare our findings with samples of field galaxies, early-stage interacting pairs, and cluster galaxies with similar data. We find that classifying the groups as dynamically "old" or "young", depending on whether or not at least one quarter of their members are early-type systems, is physical and consistent with past classifications of HCGs based on their atomic gas content. [...ABRIDGED...] We also examine their SF properties, UV-optical and mid-IR colors, and we conclude that all the evidence point to an evolutionary scenario in which the effects of the group environment and the properties of the galaxy members are not instantaneous. Early on, the influence of close companions to group galaxies is similar to the one of galaxy pairs in the field. However, as the time progresses, the effects of tidal torques and minor merging, shape the morphology and star formation history of the group galaxies, leading to an increase of the fraction of early-type members and a rapid built up of the stellar mass in the remaining late-type galaxies.

astro-ph.CO↗

arXiv2011

Testing the Unification Model for AGN in the Infrared: are the obscuring tori of Type 1 and 2 Seyferts different?

We present new mid-infrared (MIR) imaging data for three Type-1 Seyfert galaxies obtained with T-ReCS on the Gemini-South Telescope at subarcsecond resolution. Our aim is to enlarge the sample studied in a previous work to compare the properties of Type-1 and Type-2 Seyfert tori using clumpy torus models and a Bayesian approach to fit the infrared nuclear spectral energy distributions (SEDs). Thus, the sample considered here comprises 7 Type-1, 11 Type-2, and 3 intermediate-type Seyferts. The unresolved IR emission of the Seyfert 1 galaxies can be reproduced by a combination of dust heated by the central engine and direct AGN emission, while for the Seyfert 2 nuclei only dust emission is considered. These dusty tori have physical sizes smaller than 6 pc radius, as derived from our fits. Unification schemes of AGN account for a variety of observational differences in terms of viewing geometry. However, we find evidence that strong unification may not hold, and that the immediate dusty surroundings of Type-1 and Type-2 Seyfert nuclei are intrinsically different. The Type-2 tori studied here are broader, have more clumps, and these clumps have lower optical depths than those of Type-1 tori. The larger the covering factor of the torus, the smaller the probability of having direct view of the AGN, and vice-versa. In our sample, Seyfert 2 tori have larger covering factors and smaller escape probabilities than those of Seyfert 1. All the previous differences are significant according to the Kullback-Leibler divergence. Thus, on the basis of the results presented here, the classification of a Seyfert galaxy as a Type-1 or Type-2 depends more on the intrinsic properties of the torus rather than on its mere inclination towards us, in contradiction with the simplest unification model.

astro-ph.CO↗

arXiv2010

The Nuclear Structure in Nearby Luminous Infrared Galaxies: HST NICMOS Imaging of the GOALS Sample

We present results of Hubble Space Telescope NICMOS H-band imaging of 73 of most luminous (i.e., log[L_IR/L_0]>11.4) Infrared Galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey (GOALS). This dataset combines multi-wavelength imaging and spectroscopic data from space (Spitzer, HST, GALEX, and Chandra) and ground-based telescopes. In this paper we use the high-resolution near-infrared data to recover nuclear structure that is obscured by dust at optical wavelengths and measure the evolution in this structure along the merger sequence. A large fraction of all galaxies in our sample possess double nuclei (~63%) or show evidence for triple nuclei (~6%). Half of these double nuclei are not visible in the HST B-band images due to dust obscuration. The majority of interacting LIRGs have remaining merger timescales of 0.3 to 1.3 Gyrs, based on the projected nuclear separations and the mass ratio of nuclei. We find that the bulge luminosity surface density increases significantly along the merger sequence (primarily due to a decrease of the bulge radius), while the bulge luminosity shows a small increase towards late merger stages. No significant increase of the bulge Sersic index is found. LIRGs that show no interaction features have on average a significantly larger bulge luminosity, suggesting that non merging LIRGs have larger bulge masses than merging LIRGs. This may be related to the flux limited nature of the sample and the fact that mergers can significantly boost the IR luminosity of otherwise low luminosity galaxies. We find that the projected nuclear separation is significantly smaller for ULIRGs (median value of 1.2 kpc) than for LIRGs (mean value of 6.7 kpc), suggesting that the LIRG phase appears earlier in mergers than the ULIRG phase.

astro-ph.CO↗

arXiv2010

The Spatial Extent of (U)LIRGs in the mid-Infrared I: The Continuum Emission

We present an analysis of the extended mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey (GOALS) sample based on 5-15um low resolution spectra obtained with the IRS on Spitzer. We calculate the fraction of extended emission as a function of wavelength for the galaxies in the sample, FEE_lambda. We can identify 3 general types of FEE_lambda: one where it is constant, one where features due to emission lines and PAHs appear more extended than the continuum, and a third which is characteristic of sources with deep silicate absorption at 9.7um. More than 30% of the galaxies have a median FEE_lambda larger than 0.5 implying that at least half of their MIR emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range of FEE in their warm dust continuum (0<=FEE_13.2um<=0.85). The large values of FEE_13.2um that we find in many LIRGs suggest that their extended MIR continuum emission originates in scales up to 10kpc. The mean size of the LIRG cores at 13.2um is 2.6kpc. However, once the LIR of the systems reaches the threshold of ~10^11.8Lsun, all sources become clearly more compact, with FEE_13.2um<=0.2, and their cores are unresolved. Our estimated upper limit for the core size of ULIRGs is less than 1.5kpc. The analysis indicates that the compactness of systems with LIR>~10^11.25Lsun strongly increases in those classified as mergers in their final stage of interaction. The FEE_13.2um is also related to the contribution of an active galactic nucleus (AGN) to the MIR. Galaxies which are more AGN-dominated are less extended, independently of their LIR. We finally find that the extent of the MIR continuum emission is correlated with the far-IR IRAS log(f_60um/f_100um) color. This enables us to place a lower limit to the area in a galaxy from where the cold dust emission may originate, a prediction which can be tested soon with the Herschel Space Telescope.

astro-ph.CO↗

arXiv2010

A mid-IR study of Hickson Compact Groups I : Probing the Effects of Environment in Galaxy Interactions

Hickson Compact Groups (HCGs) are among the densest galaxy environments of the local universe. To examine the effects of the environment on the infrared properties of these systems, we present an analysis of Spitzer and ISO mid-infrared imaging as well as deep ground based near-infrared imaging of 14 HCGs containing a total of 69 galaxies. Based on mid-infrared color diagnostics we identify the galaxies which appear to host an active nucleus, while using a suite of templates, we fit the complete infrared spectral energy distribution for each group member. We compare our estimates of galaxy mass, star formation rate, total infrared luminosities, and specific star formation rates (sSFR) for our HCG sample, to samples of isolated galaxies and interacting pairs and find that overall there is no discernible difference among them. However, HCGs which can be considered as dynamically "old", host late-type galaxies with a slightly lower sSFR than the one found in dynamically "young" groups. This could be attributed to multiple past interactions among the galaxies in old groups, that have led to the build up of their stellar mass. It is also consistent with our prediction for the presence of diffuse cold dust in the intergalactic medium of 9 of the dynamically "old" groups.

astro-ph.CO↗

arXiv2010

Extreme Starbursts in the Local Universe

The "Extreme starbursts in the local universe" workshop was held at the Insituto de Astrofisica de Andalucia in Granada, Spain on 21-25 June 2010. Bearing in mind the advent of a new generation of facilities such as JWST, Herschel, ALMA, eVLA and eMerlin, the aim of the workshop was to bring together observers and theorists to review the latest results. The purpose of the workshop was to address the following issues: what are the main modes of triggering extreme starbursts in the local Universe? How efficiently are stars formed in extreme starbursts? What are the star formation histories of local starburst galaxies? How well do the theoretical simulations model the observations? What can we learn about starbursts in the distant Universe through studies of their local counterparts? How important is the role of extreme starbursts in the hierarchical assembly of galaxies? How are extreme starbursts related to the triggering of AGN in the nuclei of galaxies? Overall, 41 talks and 4 posters with their corresponding 10 minutes short talks were presented during the workshop. In addition, the workshop was designed with emphasis on discussions, and therefore, there were 6 discussion sessions of up to one hour during the workshop. Here is presented a summary of the purposes of the workshop as well as a compilation of the abstracts corresponding to each of the presentations. The summary and conclusions of the workshop along with a description of the future prospects by Sylvain Veilleux can be found in the last section of this document. A photo of the assistants is included.

astro-ph.CO↗

arXiv2010

A High Spatial Resolution Mid-Infrared Spectroscopic Study of the Nuclei and Star-Forming Regions in Luminous Infrared Galaxies

We present a high spatial (diffraction-limited) resolution (~0.3") mid-infrared (MIR) spectroscopic study of the nuclei and star-forming regions of 4 local luminous infrared galaxies (LIRGs) using T-ReCS on the Gemini South telescope. We investigate the spatial variations of the features seen in the N-band spectra of LIRGs on scales of ~100 pc, which allow us to separate the AGN emission from that of the star formation (SF). We compare our Gemini T-ReCS nuclear and integrated spectra of LIRGs with those obtained with Spitzer IRS. The 9.7um silicate absorption feature is weaker in the nuclei of the LIRGs than in the surrounding regions. This is probably due to the either clumpy or compact environment of the central AGN or young, nuclear starburst. We find that the [NeII] luminosity surface density is tightly and directly correlated with that of Pa-alpha for the LIRG star-forming regions (slope of 1.00+-0.02). Although the 11.3um PAH feature shows also a trend with Pa-alpha, this is not common for all the regions. We also find that the [NeII]\Pa-alpha ratio does not depend on the Pa-alpha equivalent width (EW), i.e., on the age of the ionizing stellar populations, suggesting that, on the scales probed here, the [NeII] emission line is a good tracer of the SF activity in LIRGs. On the other hand, the 11.3um PAH\Pa-alpha ratio increases for smaller values of the Pa-alpha EW (increasing ages), indicating that the 11.3um PAH feature can also be excited by older stars than those responsible for the Pa-alpha emission. Additional high spatial resolution observations are essential to investigate, in a statistical way, the star formation in local LIRGs at the smallest scales and to probe ultimately whether they share the same physical properties as high-z LIRGs, ULIRGs and submillimiter galaxies.

astro-ph.CO↗

arXiv2008

Discovery of a very highly extinguished supernova in a luminous infrared galaxy

We report the discovery of a confirmed supernova (SN) and a supernova-candidate in near-infrared images from the ALTAIR/NIRI adaptive optics system on the Gemini-North Telescope and NICMOS on the Hubble Space Telescope. The Gemini images were obtained as part of a near-infrared K-band search for highly-obscured SNe in the nuclear regions of luminous infrared galaxies. SN 2008cs apparent in the Gemini images is the first SN discovered using laser guide star adaptive optics. It is located at 1500 pc projected distance from the nucleus of the luminous infrared galaxy IRAS 17138-1017. The SN luminosity, JHK colors and light curve are consistent with a core-collapse event suffering from a very high host galaxy extinction of 15.7 +- 0.8 magnitudes in V-band which is to our knowledge the highest yet measured for a SN. The core-collapse nature of SN 2008cs is confirmed by its radio detection at 22.4 GHz using our Very Large Array observations 28 days after the SN discovery, indicating a prominent interaction of the SN ejecta with the circumstellar medium. An unconfirmed SN apparent in the NICMOS images from 2004 is located in the same galaxy at 660 pc projected distance from the nucleus and has a lower extinction.

astro-ph↗

arXiv2007

Optical detection of the radio supernova SN 2000ft in the circumnuclear region of the luminous infrared galaxy NGC 7469

SN 2000ft is detected in two independent Planetary Camera images (F547W and F814W) taken May 13, 2000, about two months before the predicted date of the explosion (July 19, 2000), based on the analysis of its radio light evolution by Alberdi and collaborators. The apparent optical magnitudes and red color of SN 2000ft indicate that it is observed through an extinction of at least A$_V$= 3.0 magnitudes. The extinction corrected lower limit to the absolute visual magnitude (M$_V$ $\leq -$ 18.0), identifies SN 2000ft as a luminous supernova in the optical, as other luminous radio supernovae before. SN 2000ft exploded in a region located at only 0.1 arcsec (i.e. 34 +/- 3 pc) west of a faint cluster (C24). No parent cluster is identified within the detection limits of the HST short exposures. The unambiguous detection of SN 2000ft in the visual shows that multi-epoch sub-arcsecond (FWHM less than 0.1 arcsec) optical imaging is also a valid tool that should be explored further to detect supernovae in the dusty (circum)nuclear regions of (U)LIRGs.

astro-ph↗

arXiv2006

Mid-Infrared T-ReCS Spectroscopy of Local LIRGs

We present T-ReCS high spatial resolution N-band (8-13 micron) spectroscopy of the central regions (a few kpc) of 3 local LIRGs. The nuclear spectra show deep 9.7 micron silicate absorption feature and the high ionization [SIV]10.5 micron emission line, consistent with their optical classification as AGN. The two LIRGs with unresolved mid-IR emission do not show PAH emission at 11.3 micron in their nuclear spectra. The spatially resolved mid-IR spectroscopy of NGC 5135 allows us to separate out the spectra of the Seyfert nucleus, an HII region, and the diffuse region between them on scales of less than 2.5 arcsec ~ 600 pc. The diffuse region spectrum is characterized by strong PAH emission with almost no continuum, whereas the HII region shows PAH emission with a smaller equivalent width as well as [NeII]12.8 micron line.

astro-ph↗

arXiv2006

High spatial resolution T-ReCS mid-infrared imaging of Luminous Infrared Galaxies

We present diffraction-limited (FWHM ~ 0.3arcsec) Gemini/T-ReCS mid-infrared (MIR: N-band or narrow-band at 8.7micron) imaging of four Luminous Infrared Galaxies (LIRGs) drawn from a representative local sample. The MIR emission in the central few kpc is strikingly similar to that traced by Pa-alpha, and generally consists of bright nuclear emission and several compact circumnuclear and/or extranuclear HII regions. The central MIR emission is dominated by these powerful HII regions, consistent with the majority of AGN in this local sample of LIRGs contributing a minor part of the MIR emission. The luminous circumnuclear HII regions detected in LIRGs follow the extrapolation of the 8micron vs. Pa-alpha relation found for M51 HII knots. The integrated central 3-7kpc of galaxies, however, present elevated 8micron/Pa-alpha ratios with respect to individual HII regions, similar to the integrated values for star-forming galaxies. Our results show that the diffuse 8micron emission, not directly related to the ionizing stellar population, can be as luminous as that from the resolved HII regions. Therefore, calibrations of the star formation rate for distant galaxies should be based on the integrated 8micron emission of nearby galaxies, not that of the HII regions alone.

astro-ph↗