arXiv subjects

D. Coia

Publications and source records attributed to D. Coia.

25 records · Page 2Linked to original sources

arXiv2006

An ISOCAM survey through gravitationally lensing galaxy clusters. III. New results from mid-infrared observations of th e cluster Abell 2219

The massive cluster of galaxies Abell 2219 (z = 0.228) was observed at 14.3 $μ$m with the Infrared Space Observatory and results were published by Barvainis et al. (1999). These observations have been reanalyzed using a method specifically designed for the detection of faint sources that had been applied to other clusters. Five new sources were detected and the resulting cumulative total of ten sources all have optical counterparts. The mid-infrared sources are identified with three cluster members, three foreground galaxies, an Extremely Red Object, a star and two galaxies of unknown redshift. The spectral energy distributions (SEDs) of the galaxies are fit with models from a selection, using the program GRASIL. Best-fits are obtained, in general, with models of galaxies with ongoing star formation. For three cluster members the infrared luminosities derived from the model SEDs are between ~5.7x10^10 Lsun and 1.4x10^11 Lsun, corresponding to infrared star formation rates between 10 and 24 Msun yr^-1. The two cluster galaxies that have optical classifications are in the Butcher-Oemler region of the color-magnitude diagramme. The three foreground galaxies have infrared luminosities between 1.5x10^10 Lsun and 9.4x10^10 Lsun yielding infrared star formation rates between 3 and 16 Msun yr^-1. Two of the foreground galaxies are located in two foreground galaxy enhancements (Boschin et al. 2004). Including Abell 2219, six distant clusters of galaxies have been mapped with ISOCAM and luminous infrared galaxies (LIRGs) have been found in three of them. The presence of LIRGs in Abell 2219 strengthens the association between luminous infrared galaxies in clusters and recent or ongoing cluster merger activity.

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arXiv2006

An ISOCAM survey through gravitationally lensing galaxy clusters. IV. Luminous infrared galaxies in Cl 0024+1654 and the dynamical status of clusters

Observations of the core of the massive cluster Cl 0024+1654, at a redshift z=0.39, were obtained with the Infrared Space Observatory using ISOCAM at 6.7 mum and 14.3 mum (hereafter 15 mum). Thirty five sources were detected at 15 mum and thirteen of them are spectroscopically identified with cluster galaxies. The remaining sources consist of four stars, one quasar, one foreground galaxy, three background galaxies and thirteen sources with unknown redshift. The ISOCAM sources have best-fit SEDs typical of spiral or starburst models observed 1 Gyr after the main starburst event. The median infrared luminosity of the twelve cluster galaxies is 1.0x10^11 Lsun, with 10 having infrared luminosity above 9x10^10 Lsun, and so lying near or above the 1x10^11 Lsun threshold for identification as a luminous infrared galaxy (LIRG). The [OII] star formation rates obtained for 3 cluster galaxies are one to two orders of magnitude lower than the infrared values, implying that most of the star formation is missed in the optical because it is enshrouded by dust in the starburst galaxy. The counterparts of about half of the 15 mum cluster sources are blue, luminous, star-forming systems and the type of galaxy that is usually associated with the Butcher-Oemler effect. Dust obscuration may be a major cause of the 15 mum sources appearing on the cluster main sequence. The majority of the ISOCAM sources in the Butcher-Oemler region of the colour-magnitude diagram are best fit by spiral-type SEDs whereas post-starburst models are preferred on the main sequence, with the starburst event probably triggered by interaction with one or more galaxies. Finally, the mid-infrared results on Cl 0024+1654 are compared with four other clusters observed with ISOCAM.

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arXiv2005

ISO observations of the interacting galaxy Markarian 297: with the powerful supernova remnant 1982aa

Markarian (Mkn) 297 is a complex system with two interacting galaxies. Observations were made with ISO using ISOCAM, ISOPHOT and LWS. We present ISOCAM maps at 6.7, 7.7, 12 and 14.3 microns which, with PHT-S spectrometry of the central interacting region, probe the dust obscured star formation and dust properties. ISOCAM reveals that the strongest emission region in the four MIR bands is completely unremarkable at visible and near-IR (e.g. 2MASS) wavelengths, and does not coincide with the nuclear region of either colliding galaxy. It shares this striking characteristic with the overlap region of the colliding galaxies in the Antennae (NGC 4038, 4039), the intragroup region of Stephan's Quintet, and IC 694 in the interacting system Arp 299. At 15 microns, the hidden source in Mkn 297 is, respectively, 14.6 and 3.8 times more luminous than the hidden sources in the Antennae (NGC 4038/4039) and Stephan's Quintet. Numerical simulations indicate that we see the Mkn 297 interaction about 1.5 x 10e8 years after the collision. ISOCAM shows knots and ridges of emission. The 14.3/7.7 micron ratio map implies widespread strong star formation. Strong emission features were detected in the ISOPHOT spectrum, while [OI], [OIII] and [CII] emission lines were seen with LWS. Using data from the three instruments, luminosities and masses for two dust components were determined. The total infrared luminosity is approximately 10e11 L_sol, marginally a LIRG. A 1979 supernova generated one of the most powerful known radio remnants (SN 1982aa) close to the strongest MIR source and identified with star forming region 14 in the optical. This exceptional supernova explosion may have been accompanied by a GRB, and a search for a GRB in this direction in contemporaneous satellite data is recommended.

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arXiv2005

ISO observations of the Wolf-Rayet galaxies NGC 5430, NGC 6764, Mrk 309 and VII Zw 19

Observations of four WR galaxies (NGC 5430, NGC 6764, Mrk 309 and VII Zw 19) using the Infrared Space Observatory are presented here. ISOCAM maps of NGC 5430, Mrk 309 and NGC 6764 revealed the location of star formation regions in each of these galaxies. ISOPHOT spectral observations from 4 to 12 microns detected the ubiquitous PAH bands in the nuclei of the targets and several of the disk star forming regions, while LWS spectroscopy detected [OI] and [CII] emission lines from two galaxies, NGC 5430 and NGC 6764. Using a combination of ISO and IRAS flux densities, a dust model based on the sum of modified blackbody components was successfully fitted to the available data. These models were then used to calculate new values for the total IR luminosities for each galaxy, the size of the various dust populations, and the global SFR. The derived flux ratios, the SFRs, the high L(PAH)/L(40-120 microns) and F(PAH 7.7 microns)/F(7.7 microns continuum) values suggest that most of these galaxies are home to only a compact burst of star formation. The exception is NGC 6764, whose F(PAH 7.7 microns)/F(7.7 microns continuum) value of 1.22 is consistent with the presence of an AGN, yet the L(PAH)/L(40-120 microns) is more in line with a starburst, a finding in line with a compact low-luminosity AGN dominated by the starburst.

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arXiv2004

ISOCAM Observations of Intermediate-redshift Galaxy Clusters at 7 and 15 microns

The gravitationally lensing clusters A370, A2218, A1689 and CL0024+1654 were observed with the Infrared Space Observatory (ISO) using ISOCAM at 6.7 and 14.3 microns (hereafter 7 and 15 microns respectively). A total of 178 sources were detected in the whole set, 70 of them being cluster objects. The spectral energy distribution of a subset of sources was calculated using GRASIL. The results for the total infrared luminosity and the estimation of the star formation rate are presented for the non stellar objects for which the SED has been determined. The majority of the cluster galaxies in A2218 are best fit by models of quiescent ellipticals. In Cl0024+1654, most of the galaxies lying on the Butcher-Oemler region of the colour-magnitude diagram are best fit by disk galaxies, while those on the main sequence area have in general SEDs corresponding to post-starburst galaxies. The population of each cluster is compared with the field population, as well as with the population of other clusters. A significant number of Luminous IR Galaxies (LIRGs) is detected in CL0024+1654, while only one LIRG has been observed in total in A370, A1689, and A2218. This result supports the link between LIRGs in clusters and recent or ongoing cluster merger activity as well as the need for extending the observations to the outer parts of clusters.

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arXiv2004

An ISOCAM survey through gravitationally lensing galaxy clusters. II. The properties of infrared galaxies in the A2218 field

We observed the cluster Abell 2218 (z=0.175), with ISOCAM on board the Infrared Space Observatory, using two filters with reference wavelengths of 6.7 and 14.3 microns. We detected 67 extragalactic mid-infrared sources. Using the ``GRASIL'' models of Silva et al. (1998) we have obtained acceptable and well constrained fits to the observed spectral energy distributions (SEDs) of 41 of these sources, for which additional optical/near-infrared magnitudes, and, in some cases, redshifts, were available. We have then determined the total infrared luminosities and star formation rates (SFRs) of these 41 sources, of which 27 are cluster members and 14 are field galaxies at a median redshift z~0.6. The SEDs of most of the ISOCAM cluster members are best fit by models with negligible star formation in the last ~1 Gyr. The 7 faintest cluster members have a slightly higher, but still very mild, star-formation activity. The ISOCAM-selected cluster galaxies appear to be an unbiased subsample of the overall cluster population. If A2218 is undergoing a merger, as suggested by some optical and X-ray analyses, then this merger does not seem to affect the mid-infrared properties of its galaxies. The SEDs of most ISOCAM-selected field sources are best fit by models with significant ongoing (and recent) star formation, resembling those of massive star-forming spirals or (post)starburst galaxies. Their median SFR is 22 solar masses per year. Eight of the 14 field sources are Luminous IR Galaxies. (Abridged)

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arXiv2004

Clusters of galaxies in the mid-infrared

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.

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