History of the Geology and Geography Department, Ohio Wesleyan University

Author Institution: Department of Geology and Geography, Ohio Wesleyan Universit

The Stellar Population of Stripped Cluster Spiral NGC 4522: A Local Analog to K+A Galaxies?

We present observations of the stripped Virgo Cluster spiral NGC 4522, a clear, nearby example of a galaxy currently undergoing ISM-ICM stripping. Utilizing SparsePak integral field spectroscopy on the WIYN 3.5m telescope and GALEX UV photometry, we present an analysis of the outer disk (r > 3 kpc) stellar population of this galaxy, beyond the HI and Halpha truncation radius. We find that the star formation in the gas-stripped outer disk ceased very recently, ~100 Myr ago, in agreement with previous claims that this galaxy is currently being stripped. At the time of this stripping, data and models suggest that the galaxy experienced a modest starburst. The stripping is occurring in a region of the cluster well outside the cluster core, likely because this galaxy is experiencing extreme conditions from a dynamic ICM due to an ongoing sub-cluster merger. The outer disk has a spectrum of a K+A galaxy, traditionally observed in high-redshift cluster galaxies. In the case of NGC 4522, a K+A spectrum is formed by simple stripping of the interstellar gas by the hot intracluster medium. These data show K+A spectra can be created by cluster processes and that these processes likely extend beyond the cluster core.Comment: 5 pages, 3 figures, accepted for publication in ApJ Letter

VIVA, VLA Imaging of Virgo spirals in Atomic gas: I. The Atlas & The HI Properties

We present the result of a new VLA HI Imaging survey of Virgo galaxies, VIVA (the VLA Imaging survey of Virgo galaxies in Atomic gas). The survey includes high resolution HI data of 53 carefully selected late type galaxies (48 spirals and 5 irregular systems). The goal is to study environmental effects on HI gas properties of cluster galaxies to understand which physical mechanisms affect galaxy evolution in different density regions, and to establish how far out the impact of the cluster reaches. As a dynamically young cluster, Virgo contains examples of galaxies experiencing a variety of environmental effects. Its nearness allows us to study each galaxy in great detail. We have selected Virgo galaxies with a range of star formation properties in low to high density regions (at the projected distance from M87, d_87=0.3-3.3 Mpc). Contrary to pr evious studies, more than half of the galaxies in the sample (~60%) are fainter than 12 mag in B_T. Overall, the selected galaxies represent the late type Virgo galaxies (S0/a to Sd/Irr) down to m_p<~14.6 fairly well in morphological type, systemic velocity, subcluster membership, HI mass and deficiency. In this paper (VIVA I: the atlas and the HI properties), we present HI maps and properties, and describe the HI morphology and kinematics of individual galaxies in detail (abbreviated).Comment: K band magnitudes for 6 galaxies in Table 3 have been corrected. One of the labels in Figure 8 is corrected and an omission in the acknowledgments has been added. The latter two were correct in the previous astro-ph version but are wrong in the journal version. A full resolution with the complete HI atlas can be downloaded at http://www.astro.yale.edu/viva/pub.htm

Environmental Effects in Clusters: Modified Far-Infrared--Radio Relations within Virgo Cluster Galaxies

(abridged) We present a study on the effects of the intracluster medium (ICM) on the interstellar medium (ISM) of 10 Virgo cluster spiral galaxies using {\it Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the FIR-radio correlation within normal galaxies, we use our infrared data to create model radio maps which we compare to the observed radio images. For 6 of our sample galaxies we find regions along their outer edges that are highly deficient in the radio compared with our models. We believe these observations are the signatures of ICM ram pressure. For NGC 4522 we find the radio deficit region to lie just exterior to a region of high radio polarization and flat radio spectral index, although the total 20 cm radio continuum in this region does not appear strongly enhanced. These characteristics seem consistent for other galaxies with radio polarization data in the literature. The strength of the radio deficit is inversely correlated with the time since peak pressure as inferred from stellar population studies and gas stripping simulations, suggesting the strength of the radio deficit is good indicator of the strength of the current ram pressure. We also find that galaxies having {\it local} radio {\it deficits} appear to have {\it enhanced global} radio fluxes. Our preferred physical picture is that the observed radio deficit regions arise from the ICM wind sweeping away cosmic-ray (CR) electrons and the associated magnetic field, thereby creating synchrotron tails as observed for some of our galaxies. We propose that CR particles are also re-accelerated by ICM-driven shocklets behind the observed radio deficit regions which in turn enhances the remaining radio disk brightness.Comment: 19 pages, 10 figures; Astrophysical Journa

HI Distribution and Tully-Fisher Distances of Gas-Poor Spiral Galaxies in the Virgo Cluster Region

We present aperture synthesis observations in the 21 cm line of pointings centered on the Virgo Cluster region spirals NGC 4307, NGC 4356, NGC 4411B, and NGC 4492 using the Very Large Array (VLA) radiotelescope in its CS configuration. These galaxies were identified in a previous study of the three-dimensional distribution of HI emission in the Virgo region as objects with a substantial dearth of atomic gas and Tully-Fisher (TF) distance estimates that located them well outside the main body of the cluster. We have detected two other galaxies located in two of our fields and observed bands, the spiral NGC 4411A and the dwarf spiral VCC 740. We provide detailed information of the gas morphology and kinematics for all these galaxies. Our new data confirm the strong HI-deficiency of all the main targets but NGC 4411B, which is found to have a fairly normal neutral gas content. The VLA observations have also been used to discuss the applicability of TF techniques to the five largest spirals we have observed. We conclude that none of them is actually suitable for a TF distance evaluation, whether due to the radical trimming of their neutral hydrogen disks (NGC 4307, NGC 4356, and NGC 4492) or to their nearly face-on orientation (NGC 4411A and B).Comment: 32 pages, 5 figures. Accepted for publication in A

Star formation history and X-ray binary populations: the case of the Small Magellanic Cloud

Using Chandra, XMM-Newton, and optical photometric catalogs we study the young X-ray binary (XRB) populations of the Small Magellanic Cloud. We find that the Be/X-ray binaries (Be-XRBs) are observed in regions with star formation rate bursts ~25-60 Myr ago. The similarity of this age with the age of maximum occurrence of the Be phenomenon (~40 Myr) indicates that the presence of a circumstellar decretion disk plays a significant role in the number of observed XRBs in the 10-100 Myr age range. We also find that regions with strong but more recent star formation (e.g., the Wing) are deficient in Be-XRBs. By correlating the number of observed Be-XRBs with the formation rate of their parent populations, we measure a Be-XRB production rate of ~1 system per 3 x 10^(-3) M$_{\odot}$/yr. Finally, we use the strong localization of the Be-XRB systems in order to set limits on the kicks imparted on the neutron star during the supernova explosion.Comment: 15 pages, 2 figures, published in ApJ Letter