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(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 Journal

Deep wide-field H$\alpha$+[NII] imaging around the Virgo cluster giant elliptical galaxy M86 reveals a highly complex and disturbed ISM/ICM. The most striking feature is a set of H$\alpha$ filaments which clearly connect M86 with the nearby disturbed spiral NGC 4438 (23$'$=120 kpc projected away), providing strong evidence for a previously unrecognized collision between them. Spectroscopy of selected regions show a fairly smooth velocity gradient between M86 and NGC 4438, consistent with the collision scenario. Such a collision would impart significant energy into the ISM of M86, probably heating the gas and acting to prevent the gas from cooling to form stars. We propose that cool gas stripped from NGC 4438 during the collision and deposited in its wake is heated by shocks, ram pressure drag, or thermal conduction, producing most of the H$\alpha$ filaments. Some H$\alpha$ filaments are associated with the well-known ridge of bright X-ray emission to the NW of the nucleus, suggesting that the collision is responsible for peculiarities of M86 previously ascribed to other effects. M86 is radio-quiet, thus AGN heating is unlikely to play a significant role. The M86 system has implications for understanding the role of gravitational interactions in the heating of the ISM in ellipticals, and how collisions in clusters transform galaxies., Comment: 6 pages, 2 figures. For high-resolution images, see http://www.astro.yale.edu/tal/research/index.html

We present results on the interstellar medium (ISM) properties of 29 galaxies based on a comparison of {\it Spitzer} far-infrared and Westerbork Synthesis Radio Telescope radio continuum imagery. Of these 29 galaxies, 18 are close enough to resolve at $\la$1 kpc scales at 70 $\micron$ and 22 cm. We extend the \citet{ejm06a,ejm06b} approach of smoothing infrared images to approximate cosmic-ray (CR) electron spreading and thus largely reproduce the appearance of radio images. Using a wavelet analysis we decompose each 70 $\micron$ image into one component containing the star-forming {\it structures} and a second one for the diffuse {\it disk}. The components are smoothed separately, and their combination compared to a free-free corrected 22 cm radio image; the scale-lengths are then varied to best match the radio and smoothed infrared images. We find that late-type spirals having high amounts of ongoing star formation benefit most from the two-component method. We also find that the disk component dominates for galaxies having low star formation activity, whereas the structure component dominates at high star formation activity. We propose that this result arises from an age effect rather than from differences in CR electron diffusion due to varying ISM parameters. The bulk of the CR electron population in actively star-forming galaxies is significantly younger than that in less active galaxies due to recent episodes of enhanced star formation; these galaxies are observed within $\sim10^{8}$ yr since the onset of the most recent star formation episode. The sample irregulars have anomalously low best-fit scale-lengths for their surface brightnesses compared to the rest of the sample spirals which we attribute to enhanced CR electron escape., Comment: 8 pages, 2 Figures; To appear in the proceeding from "The Evolving ISM in the Milky Way and Nearby Galaxies"

We present a study on the effects of the intracluster medium (ICM) on the interstellar medium (ISM) of 10 Virgo cluster galaxies using {\it Spitzer} far-infrared (FIR) and VLA radio continuum imaging. Relying on the FIR-radio correlation {\it 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, however the total radio continuum in this region does not appear significantly enhanced. This scenario seems consistent for other galaxies with radio polarization data in the literature. We also find that galaxies having local radio deficits appear to have 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 observed for some of our galaxies. 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. The high radio polarization and lack of coincidental signatures in the total synchrotron power in these regions arises from shear, and possibly mild compression, as the ICM wind drags and stretches the magnetic field., Comment: 9 pages, 3 figures; To appear in the proceeding from "The Evolving ISM in the Milky Way and Nearby Galaxies"

VIVA HI observations of the Virgo spiral galaxy NGC 4501 are presented. The HI disk is sharply truncated to the southwest, well within the stellar disk. A region of low surface-density gas, which is more extended than the main HI disk, is discovered northeast of the galaxy center. These data are compared to existing 6cm polarized radio continuum emission, Halpha, and optical broad band images. We observe a coincidence between the western HI and polarized emission edges, on the one hand, and a faint Halpha emission ridge, on the other. The polarized emission maxima are located within the gaps between the spiral arms and the faint Halpha ridge. Based on the comparison of these observations with a sample of dynamical simulations with different values for maximum ram pressure and different inclination angles between the disk and the orbital plane,we conclude that ram pressure stripping can account for the main observed characteristics. NGC 4501 is stripped nearly edge-on, is heading southwest, and is ~200-300 Myr before peak ram pressure, i.e. its closest approach to M87. The southwestern ridge of enhanced gas surface density and enhanced polarized radio-continuum emission is due to ram pressure compression. It is argued that the faint western Halpha emission ridge is induced by nearly edge-on ram pressure stripping. NGC 4501 represents an especially clear example of early stage ram pressure stripping of a large cluster-spiral galaxy., Comment: 22 pages, 25 figures, accepted for publication in A&A

We present results on the interstellar medium (ISM) properties of 29 galaxies based on a comparison of {\it Spitzer} far-infrared and Westerbork Synthesis Radio Telescope radio continuum imagery. Of these 29 galaxies, 18 are close enough to resolve at $\la$1 kpc scales at 70 $\micron$ and 22 cm. We extend the \citet{ejm06a,ejm06b} approach of smoothing infrared images to approximate cosmic-ray (CR) electron spreading and thus largely reproduce the appearance of radio images. Using a wavelet analysis we decompose each 70 $\micron$ image into one component containing the star-forming {\it structures} and a second one for the diffuse {\it disk}. The components are smoothed separately, and their combination compared to a free-free corrected 22 cm radio image; the scale-lengths are then varied to best match the radio and smoothed infrared images. We find that late-type spirals having high amounts of ongoing star formation benefit most from the two-component method. We also find that the disk component dominates for galaxies having low star formation activity, whereas the structure component dominates at high star formation activity. We propose that this result arises from an age effect rather than from differences in CR electron diffusion due to varying ISM parameters. The bulk of the CR electron population in actively star-forming galaxies is significantly younger than that in less active galaxies due to recent episodes of enhanced star formation; these galaxies are observed within $\sim10^{8}$ yr since the onset of the most recent star formation episode. The sample irregulars have anomalously low best-fit scale-lengths for their surface brightnesses compared to the rest of the sample spirals which we attribute to enhanced CR electron escape., Comment: 23 pages, 12 figures, accepted for publication in ApJ. Figure resolution slightly decreased

Using data obtained for twelve galaxies as part of the {\it Spitzer} Infrared Nearby Galaxies Survey (SINGS) and the Westerbork Synthesis Radio Telescope (WSRT)-SINGS radio continuum survey, we study how star formation activity affects the far-infrared (FIR)--radio correlation {\it within} galaxies by testing a phenomenological model, which describes the radio image as a smeared version of the FIR image. The physical basis of this description is that cosmic-ray (CR) electrons will diffuse measurably farther than the mean free path of dust-heating photons before decaying by synchrotron radiation. This description works well in general. Galaxies with higher infrared surface brightnesses have best-fit smoothing scale-lengths of a few hundred parsecs, substantially shorter than those for lower surface brightness galaxies. We interpret this result to suggest that galaxies with higher disk averaged star formation rates have had a recent episode of enhanced star formation and are characterized by a higher fraction of young CR electrons that have traveled only a few hundred parsecs from their acceleration sites in supernova remnants compared to galaxies with lower star formation activity., Comment: 5 pages, 3 figures; Accepted for publication in ApJ Letters

Using data obtained as part of the {\it Spitzer} Infrared Nearby Galaxies Survey (SINGS; Kennicutt et al. 2003) and WSRT-SINGS radio continuum survey (Braun et al. 2006), we study the effects of star-formation activity on the far-infrared (FIR)--radio correlation {\it within} galaxies. This is done by testing a phenomenological model for the correlation, which describes the radio image as a smeared version of the FIR image. We find that this description works particularly well for galaxies with higher infrared surface brightnesses, yielding best-fit smoothing scale-lengths of a few hundred parsecs, substantially shorter than those for lower surface brightness galaxies. We interpret this result to suggest that galaxies with higher disk averaged star formation rates have had a recent episode of enhanced star formation and are characterized by a higher fraction of young cosmic-ray (CR) electrons compared to galaxies with lower star formation activity., Comment: 2 pages, 1 figure; To appear in "Studying Galaxy Evolution with Spitzer and Herschel", conference held in Crete, Greece, May 2006. CUP conference series eds. V.Charmandaris, D.Rigopoulou, and N.D. Kylafis

A dynamical model including ram pressure stripping is applied to the strongly HI deficient Virgo spiral galaxy NGC 4522. A carefully chosen model snapshot is compared with existing VLA HI observations. The model successfully reproduces the large-scale gas distribution and the velocity field. However it fails to reproduce the large observed HI linewidths in the extraplanar component, for which we give possible explanations. In a second step, we solve the induction equation on the velocity fields of the dynamical model and calculate the large scale magnetic field. Assuming a Gaussian distribution of relativistic electrons we obtain the distribution of polarized radio continuum emission which is also compared with our VLA observations at 6 cm. The observed maximum of the polarized radio continuum emission is successfully reproduced. Our model suggests that the ram pressure maximum occurred only ~50 Myr ago. Since NGC 4522 is located far away from the cluster center (~1 Mpc) where the intracluster medium density is too low to cause the observed stripping if the intracluster medium is static and smooth, two scenarios are envisaged: (i) the galaxy moves very rapidly within the intracluster medium and is not even bound to the cluster; in this case the galaxy has just passed the region of highest intracluster medium density; (ii) the intracluster medium is not static but moving due to the infall of the M49 group of galaxies. In this case the galaxy has just passed the region of highest intracluster medium velocity. This study shows the strength of combining high resolution HI and polarized radio continuum emission with detailed numerical modeling of the evolution of the gas and the large-scale magnetic field., Comment: 15 pages, 11 figures, accepted for publication in A&A

We present an analysis of the far-infrared (FIR)-radio correlation within a group of nearby star-forming galaxy disks observed as part of the {\it Spitzer} Infrared Nearby Galaxies Survey (SINGS). In our study we critically test a phenomenological model for the FIR-radio correlation which describes the radio image as a smeared version of the infrared image. The physical basis for this model is that cosmic-ray electrons (CR electrons) will diffuse significant distances from their originating sources before decaying by synchrotron emission. We find that this description generally works well, improving the correlation between the radio and infrared images of our four sample galaxies by an average factor of $\sim$1.6. We also find that the best-fit smearing kernels seem to show a dependence on the ongoing star formation activity within each disk. Galaxies having lower star formation activity (NGC 2403 and NGC 3031) are best-fit using larger smearing kernels than galaxies with more active star-forming disks (NGC 5194 and NGC 6946). We attribute this trend to be due to a recent deficit of CR electron injection into the interstellar medium of galaxies with lower star formation activity throughout their disks., Comment: 4 Pages, 2 Figures, to appear in "Infrared Diagnostics of Galaxy Evolution", ASP Conference Series, Pasadena, 14-16 November 2005

Narrow-band H-alpha+[NII] and broadband R images and surface photometry are presented for a sample of 29 bright (M_B < -18) isolated S0-Scd galaxies within a distance of 48 Mpc. These galaxies are among the most isolated nearby spiral galaxies of their Hubble classifications as determined from the Nearby Galaxies Catalog (Tully 1987a)., Comment: To appear in Astrophysical Journal Supplement Series. 17 pages, including 8 atlas pages in JPEG format. Version with high resolution figures available at http://www1.union.edu/~koopmanr/preprints.html

We present a detailed study of the peculiar HI-deficient Virgo cluster spiral galaxies NGC 4064 and NGC 4424, using $^{12}$CO 1-0 interferometry, optical imaging and integral-field spectroscopic observations, in order to learn what type of environmental interactions have afected these galaxies. Optical imaging reveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shaped isophotes and shells. NGC 4064, which lies in the cluster outskirts, possesses a relatively undisturbed outer stellar disk and a central bar. In both galaxies H-alpha emission is confined to the central kiloparsec. CO observations reveal bilobal molecular gas morphologies, with H-alpha emission peaking inside the CO lobes, implying a time sequence in the star formation process.Gas kinematics reveals strong bar-like non-circular motions in the molecular gas in both galaxies, suggesting that the material is radially infalling. In NGC 4064 the stellar kinematics reveal strong bar-like non-circular motions in the central 1 kpc. On the other hand, NGC 4424 has extremely modest stellar rotation velocities (Vmax ~ 30 km s-1), and stars are supported by random motions as far out as we can measure it. The observations suggest that the peculiarities of NGC 4424 are the result of an intermediate-mass merger plus ram pressure stripping. In the case of NGC 4064, the evidence suggests an already stripped "truncated/normal" galaxy that recently suffered a minor merger or tidal interaction with another galaxy. We propose that galaxies with "truncated/compact" H-alpha morphologies such as these are the result of the independent effects of ram pressure stripping, which removes gas from the outer disk, and gravitational interactions such as mergers, which heat stellar disks, drive gas to the central kpc and increase the central mass concentrations., Comment: 42 pages, 21 figures

(Abridged) We present an initial look at the far infrared-radio correlation within the star-forming disks of four nearby, nearly face-on galaxies (NGC 2403, NGC 3031, NGC 5194, and NGC 6946). Using Spitzer MIPS imaging and WSRT radio continuum data, observed as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS), we are able to probe variations in the logarithmic 24mu/22cm (q_24) and 70mu/22cm (q_70) surface brightness ratios across each disk at sub-kpc scales. We find general trends of decreasing q_24 and q_70 with declining surface brightness and with increasing radius. The residual dispersion around the trend of q_24 and q_70 versus surface brightness is smaller than the residual dispersion around the trend of q_24 and q_70 versus radius, on average by ~0.1 dex, indicating that the distribution of star formation sites is more important in determining the infrared/radio disk appearance than the exponential profiles of disks. We have also performed preliminary phenomenological modeling of cosmic ray electron (CRe^-) diffusion using an image-smearing technique, and find that smoothing the infrared maps improves their correlation with the radio maps. Exponential kernels tend to work better than Gaussian kernels which suggests that additional processes besides simple random-walk diffusion in three dimensions must affect the evolution of CRe^-s. The best fit smoothing kernels for the two less active star-forming galaxies (NGC 2403 and NGC 3031) have much larger scale-lengths than those of the more active star-forming galaxies (NGC 5194 and NGC 6946). This difference may be due to the relative deficit of recent CRe^- injection into the interstellar medium (ISM) for the galaxies having largely quiescent disks., Comment: 41 pages including 6 tables and 12 figures; accepted for publication in the Astrophysical Journal. A full-resolution color version can be found at http://www.astro.yale.edu/murphy/a-ph/murphy_FIR-radio.pdf ; Corrected typos

Radio continuum observations at 20 and 6 cm of the highly inclined Virgo spiral galaxy NGC 4522 are presented. Both, 20 and 6 cm total emission distributions are asymmetric with an extended component to the west where extraplanar atomic gas and Halpha emission are found. The 6 cm polarized emission is located at the eastern edge of the galactic disk. Its peak is located about 1 kpc to the east of the total emission peak. We argue that this phenomena is a characteristic feature for cluster galaxies which are experiencing significant pressure from the intracluster medium. The degree of polarization decreases from the east to the west. The flattest spectral index between 20 and 6 cm coincides with the peak of the 6 cm polarized emission. These findings are consistent with a picture of a large scale shock due to ram pressure located at the east of the galaxy where cosmic rays are accelerated. We conclude that it is likely that the galaxy experiences active ram pressure., Comment: 11 pages, 11 figures. Accepted for publication in AJ

Narrow-band Halpha and broadband R images and radial profiles are presented for 63 bright spiral galaxies in the Virgo Cluster. The sample is complete for Sb-Scd galaxies with B magnitude less than 12 and inclination less than 75 degrees. Isophotal radii, disk scalelengths, concentration parameters, and integrated fluxes are derived for the sample galaxies., Comment: 46 pages, 8 figures, including 15 pages of atlas images. Higher resolution postscript versions of the image and radial profile figures are available at http://www1.union.edu/~koopmanr/preprints.html . Accepted for publication in Astrophysical Journal Supplement Series

We report on the 2.5 arcsec (400 pc) resolution CO (J = 1 -> 0) observations covering the whole length of the bar in the strongly barred late-type spiral galaxy NGC 7479. CO emission is detected only along a dust lane that traverses the whole length of the bar, including the nucleus. The emission is strongest in the nucleus. The distribution of emission is clumpy along the bar outside the nucleus, and consists of gas complexes that are unlikely to be gravitationally bound. The CO kinematics within the bar consist of two separate components. A kinematically distinct circumnuclear disk, < 500 pc in diameter, is undergoing predominantly circular motion with a maximum rotational velocity of 245 km/s at a radius of 1 arcsec (160 pc). The CO-emitting gas in the bar outside the circumnuclear disk has substantial noncircular motions which are consistent with a large radial velocity component, directed inwards. The CO emission has a large velocity gradient across the bar dust lane, ranging from 0.5 to 1.9 km/s/pc after correcting for inclination, and the projected velocity change across the dust lane is as high as 200 km/s. This sharp velocity gradient is consistent with a shock front at the location of the bar dust lane. A comparison of H-alpha and CO kinematics across the dust lane shows that although the H-alpha emission is often observed both upstream and downstream from the dust lane, the CO emission is observed only where the velocity gradient is large. We also compare the observations with hydrodynamic models and discuss star formation along the bar., Comment: 16 pages, including 10 figures. Accepted for publication in ApJ

Quantitative measures of central light concentration and star formation activity are derived from R and Halpha surface photometry of 84 bright S0-Scd Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a good correlation between these two parameters and assigned Hubble types. In the Virgo Cluster, the correlation between central light concentration and star formation activity is significantly weaker. Virgo Cluster spirals have systematically reduced global star formation with respect to isolated spirals, with severe reduction in the outer disk, but normal or enhanced activity in the inner disk. Assigned Hubble types are thus inadequate to describe the range in morphologies of bright Virgo Cluster spirals. In particular, spirals with reduced global star formation activity are often assigned misleading early-type classifications, irrespective of their central light concentrations. 45+-25% of the galaxies classified as Sa in the Virgo Cluster sample have central light concentrations more characteristic of isolated Sb-Sc galaxies. The misleading classification of low concentration galaxies with low star formation rates as early-type spirals may account for part of the excess of `early-type' spiral galaxies in clusters. Thus the morphology-density relationship is not all due to a systematic increase in the bulge-to-disk ratio with environmental density., Comment: Accepted for publication in ApJ Letters. Latex aaspp4.sty, 9 pages, 2 Postscript (embedded) figures. Also available at http://www.astro.yale.edu/koopmann/preprint.html