arXiv subjects

Arunav Kundu

Publications and source records attributed to Arunav Kundu.

58 records · Page 4Linked to original sources

arXiv2002

The Low-Mass X-ray Binary-Globular Cluster connection in NGC 4472

We have analyzed the low mass X-ray binary (LMXB) candidates in a Chandra observation of the giant elliptical galaxy NGC 4472. In a region observed by the Hubble Space Telescope, approximately 40% of the bright (L_X >= 10^37 ergs/s) LMXBs are associated with optically identified globular clusters (GC). This is significantly higher than the fraction of bright LMXBs in Galactic GCs and confirms that GCs are the dominant sites of LMXB formation in early type galaxies. The approximately 4% of NGC 4472 GCs hosting bright LMXBs, on the other hand, is remarkably similar to the fraction of GCs with LMXBs in every other galaxy. Although statistical tests suggest that the luminosity of a cluster is an important driver of LMXB formation in GCs, this appears largely to be a consequence of the greater number of stars in bright clusters. The metallicity of GCs is a strong determinant of LMXB specific frequency, with metal-rich clusters about 3 times more likely to host LMXBs than metal-poor ones. There are weaker dependences on the size of a GC and its distance from the center of the galaxy. The X-ray luminosity does not depend significantly on the properties of the host GC. Furthermore, the spatial distribution and X-ray luminosity function of LMXBs within and outside GCs are indistinguishable. The X-ray luminosity function of both GC-LMXBs and non-GC-LMXBs reveal a break at approximately 3x10^38 ergs/s strongly suggesting that the brightest LMXBs are black hole accretors.

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arXiv2001

New Insights from HST Studies of Globular Cluster Systems II: Analysis of 29 S0 Systems

We examine the globular cluster systems (GCS) of a sample of 34 S0 galaxies from a WFPC2 snapshot survey in the V and I-bands. Of these 34 galaxies, 29 have measurable globular cluster systems. The mean color of the GCSs of individual galaxies vary from V-I=0.85 mag to V-I=1.17 mag. The average color of GCSs in all 29 S0 galaxies, V-I=1.00 +/- 0.07 mag, is similar to the value of V-I=1.04 +/- 0.04 derived for ellipticals in a companion paper. The mean metallicity of a cluster system is correlated to the luminosity (or mass) of the host galaxy, but is not dependent on the Hubble type. Our measurements of the local specific frequency, on the other hand, confirm that the cluster formation efficiency is a function of Hubble type. The mean local specific frequency of our sample within the WFPC2 field-of-view is 1.0 +/- 0.6, lower than S_(N Local)=2.4 +/- 1.8 derived for ellipticals in a similar analysis. Although we are able to confirm a bimodal color distribution in only one galaxy from the shallow 'snapshot' images analyzed in this paper statistical tests suggest that 10-20% of S0s are bimodal it at the present level of photometric accuracy. There are no significant trends in GCS properties with membership or location of the S0 host in a galaxy cluster. We have measured the turnover luminosity of the globular cluster luminosity function (GCLF) for the richest few GCSs and find the GCLF distances to be in agreement with other estimates. The globular clusters in S0 galaxies have average half-light radii of ~2.6 pc which is similar to that of other galaxies, including our own.

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arXiv2001

New Insights from HST Studies of Globular Cluster Systems I: Colors, Distances and Specific Frequencies of 28 Elliptical Galaxies

We present an analysis of the globular cluster systems of 28 elliptical galaxies using archival WFPC2 images in the V and I-bands. The V-I color distributions of at least 50% of the galaxies appear to be bimodal {\it at the present level of photometric accuracy}. We argue that this is indicative of multiple epochs of cluster formation early in the history of these galaxies, possibly due to mergers. We also present the first evidence of bimodality in low luminosity galaxies and discuss its implication on formation scenarios. The mean color of the 28 cluster systems studied by us is V-I = 1.04$\pm$0.04 (0.01) mag corresponding to a mean metallicity of Fe/H = -1.0$\pm$0.19 (0.04). We find that the turnover magnitudes of the globular cluster luminosity functions (GCLF) of our sample are in excellent agreement with the distance measurements using other methods and conclude that the accuracy of the GCLF is at least as good as the surface brightness fluctuation method. The absolute magnitude of the turnover luminosity of the GCLF is M$_V^0$ = -7.41 (0.03) in V and M$_I^0$ = -8.46 (0.03) in I. The mean local specific frequency of our sample of elliptical galaxies within the WFPC2 field-of-view is 2.4$\pm$1.8 (0.4), considerably higher than the 1.0$\pm$0.6 (0.1) derived for a comparable sample of S0s in a similar analysis. It shows no obvious correlation with metallicity, host galaxy mass or membership in a galaxy cluster. The median size of clusters in all galaxies appears to be remarkably constant at $\sim$2.4 pc. We suggest that in the future it might be possible to use the sizes of clusters in the inner regions of galaxies as a simple geometrical distance indicator.

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arXiv2000

From Globular Clusters to Tidal Dwarfs: Structure Formation in Tidal Tails

Star clusters can be found in galaxy mergers, not only in central regions, but also in the tidal debris. In both the Eastern and Western tidal tails of NGC 3256 there are dozens of young star clusters, confirmed by their blue colors and larger concentration index as compared to sources off of the tail. Tidal tails of other galaxy pairs do not have such widespread cluster formation, indicating environmental influences on the process of star formation or the packaging of the stars.

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