An Infrared Survey of Brightest Cluster Galaxies. I. (original) (raw)
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The Astrophysical …, 2008
presented an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray luminous clusters. They found that at least half of these sources have signs of excess infrared emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star forming galaxies. The gas depletion time scale is about 1 Gyr. The physical extent of the infrared excess is consistent with that of the optical emission line nebulae. This supports the hypothesis that the star formation occurs in molecular gas associated with the emission line nebulae and with evidence that the emission line nebulae are mainly powered by ongoing star
Nearby Luminous Infrared Galaxies
2016
We present the results of a ground-based, high spatial resolution infrared 18 µm imaging study of nearby luminous infrared galaxies (LIRGs), using the Subaru 8.2-m and Gemini South 8.1-m telescopes. The diffraction-limited images routinely achieved with these telescopes in the Q-band (17-23 µm) allow us to investigate the detailed spatial distribution of infrared emission in these LIRGs. We then investigate whether the emission surface brightnesses are modest, as observed in starbursts, or are so high that luminous active galactic nuclei (AGNs; high emission surface brightness energy sources) are indicated. The sample consists of 18 luminous buried AGN candidates and starburst-classified LIRGs identified in earlier infrared spectroscopy. We find that the infrared 18 µm emission from the buried AGN candidates is generally compact, and the estimated emission surface brightnesses are high, sometimes exceeding the maximum value observed in and theoretically predicted for a starburst phenomenon. The starburst-classified LIRGs usually display spatially extended 18 µm emission and the estimated emission surface brightnesses are modest, within the range sustained by a starburst phenomenon. The general agreement between infrared spectroscopic and imaging energy diagnostic methods suggests that both are useful tools for understanding the hidden energy sources of the dusty LIRG population.
Mid- to far-infrared properties of star-forming galaxies and active galactic nuclei
Astronomy & Astrophysics, 2013
We study the mid-to far-IR properties of a 24 µm-selected flux-limited sample (S 24 > 5 mJy) of 154 intermediate redshift ( z ∼ 0.15), infrared luminous galaxies, drawn from the 5 Milli-Jansky Unbiased Spitzer Extragalactic Survey. By combining existing mid-IR spectroscopy and new Herschel SPIRE submm photometry from the Herschel Multi-tiered Extragalactic Survey, we derived robust total infrared luminosity (L IR ) and dust mass (M dust ) estimates and infered the relative contribution of the AGN to the infrared energy budget of the sources. We found that the total (8−1000 µm) infrared emission of galaxies with weak 6.2 µm PAH emission (EW 6.2 ≤ 0.2 µm) is dominated by AGN activity, while for galaxies with EW 6.2 > 0.2 µm more than 50% of the L IR arises from star formation. We also found that for galaxies detected in the 250-500 µm Herschel bands an AGN has a statistically insignificant effect on the temperature of the cold dust and the far-IR colours of the host galaxy, which are primarily shaped by star formation activity. For starforming galaxies we reveal an anti-correlation between the L IR -to-rest-frame 8 µm luminosity ratio, IR8 ≡ L IR /L 8 and the strength of PAH features. We found that this anti-correlation is primarily driven by variations in the PAHs emission, and not by variations in the 5−15 µm mid-IR continuum emission. Using the [Ne iii]/[Ne ii] line ratio as a tracer of the hardness of the radiation field, we confirm that galaxies with harder radiation fields tend to exhibit weaker PAH features, and found that they have higher IR8 values and higher dust-mass-weighted luminosities (L IR /M dust ), the latter being a proxy for the dust temperature (T d ). We argue that these trends originate either from variations in the environment of the star-forming regions or are caused by variations in the age of the starburst. Finally, we provide scaling relations that will allow estimating L IR , based on single-band observations with the mid-infrared instrument, on board the upcoming James Webb space telescope.
Clusters of galaxies in the mid-infrared
2004
We describe the results of observations of galaxy clusters conducted with ISOCAM on-board the Infrared Space Observatory. Our research is aimed at understanding the processes driving galaxy evolution in dense environments, free from the bias of dust extinction. The results reveal quite a complex picture: the star-formation activity of cluster galaxies does not show a simple evolution with redshift, but also depends on the dynamical status and evolutionary history of the clusters.
A panoramic mid-infrared survey of two distant clusters
2006
We present panoramic Spitzer MIPS 24-µm observations covering ∼9×9 Mpc (25 ′ × 25 ′ ) fields around two massive clusters, Cl 0024+16 and MS 0451−03, at z = 0.39 and z = 0.55 respectively, reaching a 5-σ flux limit of ∼ 200µJy. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turn-around radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24µm members. The much more significant excess is associated with Cl 0024+16, whereas MS 0451−03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl 0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to A V ∼ 1-2 mags) rather than emission from dusty tori around active galactic nuclei (AGN) in early-type hosts. We compare the star-formation rates derived from the total infrared (8-1000µm) luminosities for the mid-infrared sources in Cl 0024+16 with those estimated from a published Hα survey, finding rates > ∼ 5× than those found from Hα, indicating significant obscured activity in the cluster population. Compared to previous mid-infrared surveys of clusters from z ∼ 0-0.5, we find evidence for strong evolution of the level of dust-obscured star-formation in dense environments to z = 0.5, analogous to the rise in fraction of optically-selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.
The Astrophysical Journal, 2004
We have studied the radio and far-infrared (FIR) emission from 114 galaxies in the 7 nearest clusters (< 100 Mpc) with prominent X-ray emission to investigate the impact of the cluster environment on the star formation and AGN activity in the member galaxies. The X-ray selection criterion is adopted to focus on the most massive and dynamically relaxed clusters. A large majority of cluster galaxies show an excess in radio emission over that predicted from the radio-FIR correlation, the fraction of sources with radio excess increases toward cluster cores, and the radial gradient in the FIR/radio flux ratio is a result of radio enhancement. Of the radio-excess sources, 70% are early-type galaxies and the same fraction host an AGN. The galaxy density drops by a factor of 10 from the composite cluster center out to 1.5 Mpc, yet galaxies show no change in FIR properties over this region, and show no indication of mass segregation. We have examined in detail the physical mechanisms that might impact the FIR and radio emission of cluster galaxies. While collisional heating of dust may be important for galaxies in cluster centers, it appears to have a negligible effect on the observed FIR emission for our sample galaxies. The correlations between radio and FIR luminosity and radius could be explained by magnetic compression from thermal ICM pressure. We also find that simple delayed harassment cannot fully account for the observed radio, FIR, and mid-IR properties of cluster galaxies.
The Astrophysical Journal Supplement Series, 2013
The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength study of luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution Spitzer IRS spectra covering 5-38 µm and provide a basic analysis of the mid-IR spectral properties observed for nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare the LIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (10 11 ≤ L IR /L < 10 12 ) and 22 ultraluminous (L IR /L ≥ 10 12 ) IR galaxies represents a complete subset of the IRAS Revised Bright Galaxy Sample and covers a range of merger stages, morphologies and spectral types. The majority (>60%) of the GOALS LIRGs have high 6.2 µm PAH equivalent widths (EQW 6.2µm > 0.4 µm) and low levels of silicate absorption (s 9.7µm > -1.0). There is a general trend among the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasing L IR . U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes and higher levels of dust obscuration. Together, these trends suggest that as gas & dust is funneled towards the center of a coalescing merger, the nuclei become more compact and more obscured. As a result, the dust temperature increases leading also to a steeper MIR slope. The sources that depart from these correlations have very low PAH equivalent width (EQW 6.2µm < 0.1 µm) consistent with their emission being dominated by an AGN in the MIR. These extremely low PAH equivalent width sources separate into two distinct types: relatively unobscured sources with a very hot dust component (and thus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient. The most heavily dust obscured sources are also the most compact in their MIR emission, suggesting that the obscuring (cool) dust is associated with the outer regions of the starburst and not simply a measure of the dust along the line of sight through a large, dusty disk. A marked decline is seen for the fraction of high EQW (star formation dominated) sources as the merger progresses. The decline is accompanied by an increase in the fraction of composite sources while the fraction of sources where an AGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimeter galaxies (SMGs) at z∼2, both the average GOALS LIRG and ULIRG spectra are more absorbed at 9.7 µm and the average GOALS LIRG has more PAH emission. However, when the AGN contributions to both the local GOALS LIRGs and the high-z SMGs are removed, the average local starbursting LIRG closely resembles the starburst-dominated SMGs.
The Distribution of Mid- and Far-Infrared Emission in 10 Interacting Galaxy Systems
The Astronomical Journal, 1998
A sample of 10 interacting and merging galaxy systems has been mapped at mid-infrared (10 km) and far-infrared (100È160 km) wavelengths with spatial resolutions of 4Aand 45A, respectively. The interacting and merging systems are known to be strong IRAS sources ; however, the IRAS data contain limited information concerning the distribution of infrared emission between the two galaxies in each pair and no information on the distribution within each galaxy. The observations presented here show that in Ðve of the seven paired systems, one galaxy is the dominant or the only infrared source. There is a good correlation between the Ha and infrared emission levels for these galaxies, indicating that the infrared emission is closely tied to dust heated by young stars. There is also a good spatial correlation between the Ha, infrared, and radio continuum morphologies of these systems, which further strengthens the belief that the infrared, as well as the radio emission, is associated with regions of active star formation. The 10 km emission is concentrated around the nuclei of most of these galaxies, indicating that the highest levels of current star formation activity are also conÐned to the near-nuclear regions. Some systems, however, show evidence for signiÐcant star formation activity throughout the outer disk regions of the galaxies. All the sample galaxies that are bright in the infrared also have optical indications of high levels of star formation or nuclear activity, suggesting that these conditions are necessary in order for a galaxy to exhibit excess infrared emission.
The X-ray properties of luminous infrared galaxies
AIP Conference Proceedings, 2001
We present a study of the sample of luminous infrared galaxies (LIGs, LIR > 10 11 L⊙) observed in the hard (2-10 keV) X rays. The main results are: 1) most LIGs are powered both by AGN and starburst activity; 2) the AGNs in our sample are absorbed in the infrared by a lower NH than in the X-rays or, alternatively, the dust-togas ratio is lower than galactic; 3) the study of a subsample of sources observed in the 20-200 keV band indicates that most of the AGNs hosted by the LIGs are heavily obscured up to 100 keV and, therefore, their contribution to the X-ray background must be small.
A large number of luminous infrared galaxies in the massive cluster Cl 0024+ 1654
2003
Abstract Cl 0024+ 1654 was observed with the Infrared Space Observatory using ISOCAM. Forty seven sources were detected at 14.3 microns and nineteen of them are cluster galaxies. The remaining sources consist of four stars, one quasar, four foreground galaxies, one background galaxy and 18 sources with unknown redshift. The median infrared luminosity of the nineteen cluster galaxies is 1.3 x10^+ 11 solar luminosities, with thirteen falling in the category of Luminous Infrared Galaxies.