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The spectrum of a galaxy contains information about its physical properties. Classifying spectra using templates helps elucidate the nature of a galaxy's energy sources. In this paper, we investigate the use of self-organizing maps in classifying galaxy spectra against templates. We trained semi-supervised self-organizing map networks using a set of templates covering the wavelength range from far ultraviolet to near infrared. The trained networks were used to classify the spectra of a sample of 142 galaxies with 0.5 < z < 1 and the results compared to classifications performed using K-means clustering, a supervised neural network, and chi-squared minimization. Spectra corresponding to quiescent galaxies were more likely to be classified similarly by all methods while starburst spectra showed more variability. Compared to classification using chi-squared minimization or the supervised neural network, the galaxies classed together by the self-organizing map had more similar spectra. The class ordering provided by the one-dimensional self-organizing maps corresponds to an ordering in physical properties, a potentially important feature for the exploration of large datasets., MNRAS in press; 19 pages, 22 figures

We present preliminary results on 24micron detections of luminous infrared galaxies at z>1 with the Multiband Imaging Photometer for Spitzer (MIPS). Observations were performed in the Lockman Hole and the Extended Groth Strip (EGS), and were supplemented by data obtained with the Infrared Array Camera (IRAC) between 3 and 9microns. The positional accuracy of ~2arcsec for most MIPS/IRAC detections provides unambiguous identifications of their optical counterparts. Using spectroscopic redshifts from the Deep Extragalactic Evolutionary Probe survey, we identify 24micron sources at z>1 in the EGS, while the combination of the MIPS/IRAC observations with $BVRIJHK$ ancillary data in the Lockman Hole also shows very clear cases of galaxies with photometric redshifts at 1=M*) galaxy counterparts. It is the first time that this population of luminous objects is detected up to z~2.5 in the infrared. Our work demonstrates the ability of the MIPS instrument to probe the dusty Universe at very high redshift, and illustrates how the forthcoming Spitzer deep surveys will offer a unique opportunity to illuminate a dark side of cosmic history not explored by previous infrared experiments.

We investigate the nature of a sample of 92 Spitzer/MIPS 24 micron selected galaxies in the CDFS, showing power law-like emission in the Spitzer/IRAC 3.6-8 micron bands. The main goal is to determine whether the galaxies not detected in X-rays (47% of the sample) are part of the hypothetical population of obscured AGN not detected even in deep X-ray surveys. The majority of the IR power-law galaxies are ULIRGs at z>1, and those with LIRG-like IR luminosities are usually detected in X-rays. The optical to IR spectral energy distributions (SEDs) of the X-ray detected galaxies are almost equally divided between a BLAGN SED class (similar to an optically selected QSO) and a NLAGN SED (similar to the BLAGN SED but with an obscured UV/optical continuum). A small fraction of SEDs resemble warm ULIRG galaxies (e.g., Mrk231). Most galaxies not detected in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically fainter, and possibly more obscured. Moreover, the IR power-law galaxies have SEDs significantly different from those of high-z (z_sp>1) IR (24 micron) selected and optically bright (VVDS I_AB, 43 pages, 12 figures, accepted for publication in ApJ

We present H\alpha{} fluxes, star formation rates (SFRs) and equivalent widths (EWs) for a sample of 156 nearby galaxies observed in the 12CO J=3-2 line as part of the James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey. These are derived from images and values in the literature and from new H\alpha{} images for 72 galaxies which we publish here. We describe the sample, observations and procedures to extract the H\alpha{} fluxes and related quantities. We discuss the SFR properties of our sample and confirm the well-known correlation with galaxy luminosity, albeit with high dispersion. Our SFRs range from 0.1 to 11 Msun yr-1 with a median SFR value for the complete sample of 0.2 Msun yr-1. This median values is somewhat lower than similar published measurements, which we attribute, in part, to our sample being HI-selected and, thus, not biased towards high SFRs as has frequently been the case in previous studies. Additionally, we calculate internal absorptions for the H\alpha{} line, A(H\alpha{}), which are lower than many of those used in previous studies. Our derived EWs, which range from 1 to 880\AA{} with a median value of 27\AA{}, show little dependence with luminosity but rise by a factor of five from early- to late-type galaxies. This paper is the first in a series aimed at comparing SFRs obtained from H\alpha{} imaging of galaxies with information derived from other tracers of star formation and atomic and molecular gas., Comment: Accepted for publication in MNRAS. 47 pages, 18 figures

We report the most accurate X-ray position of the X-ray source in the giant globular cluster G1 in M31 by using the Chandra X-ray Observatory, Hubble Space Telescope (HST), and Canada-France-Hawaii Telescope (CFHT). G1 is clearly detected with Chandra and by cross-registering with HST and CFHT images, we derive a 1-sigma error radius of 0.15 arcsec, significantly smaller than the previous measurement by XMM-Newton. We conclude that the X-ray emission of G1 is likely to come from within the core radius of the cluster. We have considered a number of possibilities for the origin of the X-ray emission but can rule all but two scenarios out: it could be due to either accretion onto a central intermediate-mass black hole (IMBH), or an ordinary low-mass X-ray binary (LMXB). Based on the X-ray luminosity and the Bondi accretion rate, an IMBH accreting from the cluster gas seems unlikely and we suggest that the X-rays are due to accretion from a companion. Alternatively, the probability that a 1.5 solar masses cluster LMXB lies within the 95 per cent X-ray error circle is about 0.7. Therefore we cannot rule out a single LMXB as the origin of the X-ray emission. While we cannot distinguish between different models with current observations, future high-resolution and high-sensitivity radio imaging observations will reveal whether there is an IMBH at the centre of G1., 5 pages, 1 figure, accepted for publication in MNRAS

Surface brightness profiles for 23 M31 star clusters were measured using images from the Wide Field Planetary Camera 2 on the Hubble Space Telescope, and fit to two types of models to determine the clusters' structural properties. The clusters are primarily young (~10^8 yr) and massive (~10^4.5 solar masses), with median half-light radius 7 pc and dissolution times of a few Gyr. The properties of the M31 clusters are comparable to those of clusters of similar age in the Magellanic Clouds. Simulated star clusters are used to derive a conversion from statistical measures of cluster size to half-light radius so that the extragalactic clusters can be compared to young massive clusters in the Milky Way. All three sets of star clusters fall approximately on the same age-size relation. The young M31 clusters are expected to dissolve within a few Gyr and will not survive to become old, globular clusters. However, they do appear to follow the same fundamental plane relations as old clusters; if confirmed with velocity dispersion measurements, this would be a strong indication that the star cluster fundamental plane reflects universal cluster formation conditions., AJ in press; 37 pages, 12 figures

Aims. We introduce our imaging survey of possible young massive globular clusters in M31 performed with the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). We obtained shallow (to B ~ 25) photometry of individual stars in 20 candidate clusters. We present here details of the data reduction pipeline that is being applied to all the survey data and describe its application to the brightest among our targets, van den Bergh 0 (VdB0), taken as a test case. Methods. Point spread function fitting photometry of individual stars was obtained for all the WFPC2 images of VdB0 and the completeness of the final samples was estimated using an extensive set of artificial stars experiments. The reddening, the age and the metallicity of the cluster were estimated by comparing the observed color magnitude diagram (CMD) with theoretical isochrones. Structural parameters were obtained from model-fitting to the intensity profiles measured within circular apertures on the WFPC2 images. Results. Under the most conservative assumptions, the stellar mass of VdB0 is M> 2.4 x 10^4 M_☉ , but our best estimates lie in the range ≃4-9 x 10^4 M_☉. The CMD of VdB0 is best reproduced by models having solar metallicity and age ≃25 Myr. Ages less than ≃12 Myr and greater than ≃60 Myr are clearly ruled out by the available data. The cluster has a remarkable number of red super giants (≳18) and a CMD very similar to Large Magellanic Cloud clusters usually classified as young globulars such as NGC 1850, for example. Conclusions. VdB0 is significantly brighter (≳1 mag) than Galactic open clusters of similar age. Its present-day mass and half-light radius ((r_h = 7.4 pc) are more typical of faint globular clusters than of open clusters. However, given its position within the disk of M31, it is expected to be destroyed by dynamical effects, in particular by encounters with giant molecular clouds, within the next ~4 Gyr.

We present IRAC and MIPS observations of NGC 205, the dwarf elliptical companion of M31, obtained with the Spitzer Space Telescope. The extended dust emission is spatially concentrated in three main emission regions. Based on our mid-to-far infrared flux density measurements alone, we derive a total dust mass estimate of the order of 3.2 × 10^4 M_⊙, at a temperature of ~20K. The gas mass associated with this component matches the predicted mass returned by the dying stars from the last burst of star formation in NGC 205 (~0.5 Gyr ago). Analysis of the Spitzer data combined with previous 1.1mm observations over a small central region or “Core” (18" diameter), suggest the presence of very cold (T ~ 12K) dust and a dust mass 16 times higher than is estimated from the Spitzer measurements alone. Assuming a gas to dust mass ratio of 100, these two datasets, i.e. with and without the millimeter observations, suggest a total gas mass range of 3.2 × 10^6 to 5 × 10^7 M_⊙.

A SST survey in the NOAO Deep-Wide Field in Bo\"otes provides a complete, 8-micron-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg$^2$ field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an accurate determination of the local (z, Comment: 32 pages, 12 Figures (Fig. 1, Fig. 2, and Fig. 4 are JPEG files), accepted for publication in ApJ

In this paper, we discuss the optical and X-ray spectral properties of the sources detected in a single 200-ks Chandra pointing in the Groth-Westphal Strip region. A wealth of optical photometric and spectroscopic data are available in this field providing optical identifications and redshift determinations for the X-ray population. The optical photometry and spectroscopy used here are primarily from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey with additional redshifts obtained from the literature. These are complemented with the deeper (r ≈ 26 mag) multiwaveband data (ugriz) from the Canada–France–Hawaii Telescope Legacy Survey to estimate photometric redshifts and to optically identify sources fainter than the DEEP2 magnitude limit (R_(AB)≈ 24.5 mag). We focus our study on the 2–10 keV selected sample comprising 97 sources to the limit ≈ 8 × 10^(−1)6 erg s^(−1) cm^(−2), this being the most complete in terms of optical identification rate (86 per cent) and redshift determination fraction (63 per cent; both spectroscopic and photometric). We first construct the redshift distribution of the sample which shows a peak at z≈ 1. This is in broad agreement with models where less luminous active galactic nuclei (AGNs) evolve out to z≈ 1 with powerful quasi-stellar objects (QSOs) peaking at higher redshift, z≈ 2. Evolution similar to that of broad-line QSOs applied to the entire AGN population (both types I and II) does not fit the data. We also explore the observedNH distribution of the sample and estimate a fraction of obscured AGN (N_H > 10^(22) cm^(−2)) of 48 ± 9 per cent. This is found to be consistent with both a luminosity-dependent intrinsic N_H distribution, where less luminous systems comprise a higher fraction of type II AGNs and models with a fixed ratio 2:1 between types I and II AGNs. We further compare our results with those obtained in deeper and shallower surveys. We argue that a luminosity-dependent parametrization of the intrinsic NH distribution is required to account for the fraction of obscured AGN observed in different samples over a wide range of fluxes.

We describe the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z ~ 3, using deep mid-infrared and optical observations of the extended Groth strip, obtained with IRAC and MIPS on board Spitzer and from the ground, respectively. We focus on LBGs with detections at all four IRAC bands, in particular the 26 galaxies with IRAC 8 μm band (rest-frame K-band) detections. We use stellar population-synthesis models and probe the stellar content of these galaxies. Based on best-fit continuous star formation models, we derive estimates of the stellar mass for these LBGs. As in previous studies, we find that a fraction of LBGs have very red colors and large estimated stellar masses (M_* > 5 × 10^(10) M_⊙); the current Spitzer data allow us, for the first time, to study these massive LBGs in detail. We discuss the link between these LBGs and submillimeter-luminous galaxies, and we find that the number density of these massive LBGs at high redshift is higher than predicted by current semianalytic models of galaxy evolution.

We visually and quantitatively determine the host galaxy morphologies of 94 intermediate redshift (0.2 < z < 1.2) active galactic nuclei (AGN), selected using Chandra X-ray and Spitzer mid-infrared data in the Extended Groth Strip. Using recently developed morphology measures, the second-order moment of the brightest 20% of a galaxy's flux (M_{20}) and the Gini coefficient, we find that X-ray-selected AGN mostly reside in E/S0/Sa galaxies (53^{+11}_{-10}%), while IR-selected AGN show no clear preference for host morphology. X-ray-selected AGN hosts are members of close pairs more often than the field population by a factor of 3.3+/-1.4, but most of these pair members appear to be undisturbed early-type galaxies and do not tend to show direct evidence of gravitational perturbations or interactions. Thus, the activation mechanism for AGN activity remains unknown, even for pair members., Comment: 11 pages, 2 figures, 1 table, accepted for publication in ApJL

We discuss the optical and X-ray spectral properties of the sources detected in a single 200ks Chandra pointing in the Groth-Westphal Strip region. Optical identifications and spectroscopic redshifts are primarily from the DEEP2 survey. This is complemented with deeper (r~26mag) multi-waveband data (ugriz) from the Canada France Hawaii Legacy Survey to estimate photometric redshifts and to optically identify sources fainter than the DEEP2 magnitude limit (R(AB)~24.5mag). We focus our study on the 2-10keV selected sample comprising 97 sources to the limit ~8e-16erg/s/cm2, this being the most complete in terms of optical identification rate (86%) and redshift determination fraction (63%; both spectroscopic and photometric). We first construct the redshift distribution of the sample which shows a peak at z~1. This is in broad agreement with models where less luminous AGNs evolve out to z~1 with powerful QSOs peaking at higher redshift, z~2. Evolution similar to that of broad-line QSOs applied to the entire AGN population (both type-I and II) does not fit the data. We also explore the observed N_H distribution of the sample and estimate a fraction of obscured AGN (N_H>1e22) of ~48%. This is found to be consistent with both a luminosity dependent intrinsic N_H distribution, where less luminous systems comprise a higher fraction of type-II AGNs, and models with a fixed ratio 2:1 between type-I and II AGNs. We further compare our results with those obtained in deeper and shallower surveys. We argue that a luminosity dependent parametrisation of the intrinsic N_H distribution is required to account for the fraction of obscured AGN observed in different samples over a wide range of fluxes., MNRAS in press

We visually and quantitatively determine the host galaxy morphologies of 94 intermediate redshift (0.2 < z < 1.2) active galactic nuclei (AGN), selected using Chandra X-ray and Spitzer mid-infrared data in the Extended Groth Strip. Using recently developed morphology measures, the second-order moment of the brightest 20% of a galaxy's flux (M_{20}) and the Gini coefficient, we find that X-ray-selected AGN mostly reside in E/S0/Sa galaxies (53^{+11}_{-10}%), while IR-selected AGN show no clear preference for host morphology. X-ray-selected AGN hosts are members of close pairs more often than the field population by a factor of 3.3+/-1.4, but most of these pair members appear to be undisturbed early-type galaxies and do not tend to show direct evidence of gravitational perturbations or interactions. Thus, the activation mechanism for AGN activity remains unknown, even for pair members., 11 pages, 2 figures, 1 table, accepted for publication in ApJL

Optically--faint X-ray sources (those with f_X/f_R > 10) constitute about 20% of X-ray sources in deep surveys, and are potentially highly obscured and/or at high redshift. Their faint optical fluxes are generally beyond the reach of spectroscopy. For a sample of 20 optically--faint sources in CDFS, we compile 0.4--24 um photometry, relying heavily on Spitzer. We estimate photometric redshifts for 17 of these 20 sources. We find that these AGN are optically--faint both because they lie at significantly higher redshifts (median z ~ 1.6) than most X-ray--selected AGN, and because their spectra are much redder than standard AGN. They have 2--8 keV X-ray luminosities in the Seyfert range, unlike the QSO--luminosities of optically--faint AGN found in shallow, wide--field surveys. Their contribution to the X-ray Seyfert luminosity function is comparable to that of z>1 optically--bright AGN., Accepted for publication in the Astrophysical Journal

We present deep 3.6 - 8 micron imaging of the Hubble Deep Field South with IRAC on the Spitzer Space Telescope. We study Distant Red Galaxies (DRGs) at z>2 selected by Js - Ks > 2.3 and compare them to a sample of Lyman Break Galaxies (LBGs) at z=2-3. The observed UV-to-8 micron spectral energy distributions are fit with stellar population models to constrain star formation histories and derive stellar masses. We find that 70% of the DRGs are best described by dust-reddened star forming models and 30% are very well fit with old and ``dead'' models. Using only the I - Ks and Ks - 4.5 micron colors we can effectively separate the two groups. The dead systems are among the most massive at z~2.5 (mean stellar mass = 0.8 x 10^11 Msun) and likely formed most of their stellar mass at z>5. To a limit of 0.5 x 10^11 Msun their number density is ~10 x lower than that of local early-type galaxies. Furthermore, we use the IRAC photometry to derive rest-frame near-infrared J, H, and K fluxes. The DRGs and LBGs together show a large variation (a factor of 6) in the rest-frame K-band mass-to-light ratios (M/L_K), implying that even a Spitzer 8 micron-selected sample would be very different from a mass-selected sample. The average M/L_K of the DRGs is about three times higher than that of the LBGs, and DRGs dominate the high-mass end. The M/L_K ratios and ages of the two samples appear to correlate with derived stellar mass, with the most massive galaxies being the oldest and having the highest mass-to-light ratios, similar as found in the low-redshift universe., 4 pages, 3 figures, accepted for publication in the ApJ Letters, uses emulateapj

IRAC images of M81 show three distinct morphological constituents: a smooth distribution of evolved stars with bulge, disk, and spiral arm components; a clumpy distribution of dust emission tracing the spiral arms; and a pointlike nuclear source. The bulge stellar colors are consistent with M-type giants, and the disk colors are consistent with a slightly younger population. The dust emission generally follows the blue and ultraviolet emission, but there are large areas that have dust emission without ultraviolet and smaller areas with ultraviolet but little dust emission. The former are presumably caused by extinction, and the latter may be due to cavities in the gas and dust created by supernova explosions. The nucleus appears fainter at 8 um than expected from ground-based 10 um observations made four years ago., ApJS in press (Spitzer special issue); 15 pages, 3 figures. Changes: unused references removed, numbers and labels in Table 1 changed

Infrared source counts at wavelengths 3 < lambda < 10 um cover more than 10 magnitudes in source brightness, four orders of magnitude in surface density, and reach an integrated surface density of 10^5 sources/deg^2. At m, Comment: ApJS (in press), in the Spitzer Space Telescope special issue; 14 pages, 2 color figures, 1 table (electronic only)

Infrared source counts at wavelengths 3 < lambda < 10 um cover more than 10 magnitudes in source brightness, four orders of magnitude in surface density, and reach an integrated surface density of 10^5 sources/deg^2. At m, ApJS (in press), in the Spitzer Space Telescope special issue; 14 pages, 2 color figures, 1 table (electronic only)

The IRAC shallow survey covers 8.5 square degrees in the NOAO Deep Wide-Field Survey in Bootes with 3 or more 30 second exposures per position. An overview of the survey design, reduction, calibration, star-galaxy separation, and initial results is provided. The survey includes approximately 370,000, 280,000, 38,000, and 34,000 sources brighter than the 5 sigma limits of 6.4, 8.8, 51, and 50 microJy at 3.6, 4.5, 5.8, and 8 microns respectively, including some with unusual spectral energy distributions., Comment: To appear in ApJS, Spitzer special issue. For full resolution see http://cfa-www.harvard.edu/irac/publications

We present preliminary results on 24micron detections of luminous infrared galaxies at z>1 with the Multiband Imaging Photometer for Spitzer (MIPS). Observations were performed in the Lockman Hole and the Extended Groth Strip (EGS), and were supplemented by data obtained with the Infrared Array Camera (IRAC) between 3 and 9microns. The positional accuracy of ~2arcsec for most MIPS/IRAC detections provides unambiguous identifications of their optical counterparts. Using spectroscopic redshifts from the Deep Extragalactic Evolutionary Probe survey, we identify 24micron sources at z>1 in the EGS, while the combination of the MIPS/IRAC observations with $BVRIJHK$ ancillary data in the Lockman Hole also shows very clear cases of galaxies with photometric redshifts at 1=M*) galaxy counterparts. It is the first time that this population of luminous objects is detected up to z~2.5 in the infrared. Our work demonstrates the ability of the MIPS instrument to probe the dusty Universe at very high redshift, and illustrates how the forthcoming Spitzer deep surveys will offer a unique opportunity to illuminate a dark side of cosmic history not explored by previous infrared experiments., Accepted for publication in the Spitzer Special Issue of ApJS, 4 pages, 2 figures. 1 table

We analyze the structural parameters of the largest-available sample of spatially resolved extragalactic globular clusters. The images of M31 GCs were found in a search of HST archival data, described in a companion paper. We measure the ellipticities and position angles of the clusters and conclude that the ellipticities are consistent with being caused by rotation. We find that most clusters' surface brightness distributions are well-fit by two-dimensional single-mass Michie-King models. A few clusters show possible power-law distributions characteristic of core-collapse, but the spatial resolution is not high enough to make definitive claims. As has been found for other galaxies, the metal-rich clusters are slightly smaller than the metal-poor clusters. There are strong correlations between structural properties of M31 GCs, as for Milky Way clusters, and the two populations are located close to the same `fundamental plane' in parameter space., Accepted to AJ; 33 pages including 12 figures and 3 tables

Globular clusters at the distance of M31 have apparent angular sizes of a few arcseconds. While many M31 GCs have been detected and studied from ground-based images, the high spatial resolution of HST allows much more robust detection and characterization of star cluster properties. We present the results of a search of 157 HST/WFPC2 images of M31: we found 82 previously-cataloged globular cluster candidates as well as 32 new globular cluster candidates and 20 open cluster candidates. We present images of the new candidates and photometry for all clusters. We assess existing cluster catalogs' completeness and use the results to estimate the total number of GCs in M31 as 460+/-70. The specific frequency is S_N = 1.2+/-0.2 and the mass specific frequency T = 2.4+/-0.4; these values are at the upper end of the range seen for spiral galaxies., Comment: Accepted to AJ. 33 pages with 6 figures, plus 4 separate figures

Prompted by a new catalogue of M31 globular clusters, we have collected together individual metallicity values for globular clusters in the Local Group. Although we briefly describe the globular cluster systems of the individual Local Group galaxies, the main thrust of our paper is to examine the collective properties. In this way we are simulating the dissipationless merger of the Local Group, into presumably an elliptical galaxy. Such a merger is dominated by the Milky Way and M31, which appear to be fairly typical examples of globular cluster systems of spiral galaxies. The Local Group `Elliptical' has about 700 +/- 125 globular clusters, with a luminosity function resembling the `universal' one. The metallicity distribution has peaks at [Fe/H] ~ -1.55 and -0.64 with a metal-poor to metal-rich ratio of 2.5:1. The specific frequency of the Local Group Elliptical is initially about 1 but rises to about 3, when the young stellar populations fade and the galaxy resembles an old elliptical. The metallicity distribution and stellar population corrected specific frequency are similar to that of some known early type galaxies. Based on our results, we briefly speculate on the origin of globular cluster systems in galaxies., 22 pages, Latex, 4 figures, 5 tables, submitted to A & A

The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project., Minor changes to author list and title. Comments and feedback welcome through the paper source repository: https://github.com/astropy/astropy-v2.0-paper For more information about Astropy, see http://www.astropy.org/

We analyze the structural parameters of the largest-available sample of spatially resolved extragalactic globular clusters. The images of M31 GCs were found in a search of HST archival data, described in a companion paper. We measure the ellipticities and position angles of the clusters and conclude that the ellipticities are consistent with being caused by rotation. We find that most clusters surface brightness distributions are well-fit by two-dimensional single-mass Michie-King models. A few clusters show possible power-law distributions characteristic of core-collapse, but the spatial resolution is not high enough to make definitive claims. As has been found for other galaxies, the metal-rich clusters are slightly smaller than the metal-poor clusters. There are strong correlations between structural properties of M31 GCs, as for Milky Way clusters, and the two populations are located close to the same `fundamental plane in parameter space. Comment: Accepted to AJ; 33 pages including 12 figures and 3 tables

Globular clusters at the distance of M31 have apparent angular sizes of a few arcseconds. While many M31 GCs have been detected and studied from ground-based images, the high spatial resolution of HST allows much more robust detection and characterization of star cluster properties. We present the results of a search of 157 HST/WFPC2 images of M31: we found 82 previously-cataloged globular cluster candidates as well as 32 new globular cluster candidates and 20 open cluster candidates. We present images of the new candidates and photometry for all clusters. We assess existing cluster catalogs completeness and use the results to estimate the total number of GCs in M31 as 460+/-70. The specific frequency is S_N = 1.2+/-0.2 and the mass specific frequency T = 2.4+/-0.4; these values are at the upper end of the range seen for spiral galaxies. Comment: Accepted to AJ. 33 pages with 6 figures, plus 4 separate figures

We found the first direct evidence that the Cepheid class namesake, delta Cephei, is currently losing mass. These observations are based on data obtained with the Spitzer Space Telescope in the infrared, and with the Very Large Array in the radio. We found that delta Cephei is associated with a vast circumstellar structure, reminiscent of a bow shock. This structure is created as the wind from the star interacts with the local interstellar medium. We measure an outflow velocity of ~35.5 km/s and a mass loss rate of ~1E-7 - 1E-6 Mo/yr. The very low dust content of the outflow suggests that the wind is possibly pulsation-driven, rather than dust-driven as common for other classes of evolved stars., Proceeding submitted for the 20th Stellar Pulsation Conference (Impact of New Instruments and Insights in Stellar Pulsation), Granada, Spain, September 2011

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey carried out with MegaCam at the Canada-France-Hawaii Telescope. The survey covers the whole Virgo cluster region from its core to one virial radius (104 deg^2). The sensitivity of the survey is of f(Halpha) ~ 4 x 10^-17 erg sec-1 cm^-2 (5 sigma detection limit) for point sources and Sigma (Halpha) ~ 2 x 10^-18 erg sec^-1 cm^-2 arcsec^-2 (1 sigma detection limit at 3 arcsec resolution) for extended sources, making VESTIGE the deepest and largest blind narrow-band survey of a nearby cluster. This paper presents the survey in all its technical aspects, including the survey design, the observing strategy, the achieved sensitivity in both the narrow-band Halpha+[NII] and in the broad-band r filter used for the stellar continuum subtraction, the data reduction, calibration, and products, as well as its status after the first observing semester. We briefly describe the Halpha properties of galaxies located in a 4x1 deg^2 strip in the core of the cluster north of M87, where several extended tails of ionised gas are detected. This paper also lists the main scientific motivations of VESTIGE, which include the study of the effects of the environment on galaxy evolution, the fate of the stripped gas in cluster objects, the star formation process in nearby galaxies of different type and stellar mass, the determination of the Halpha luminosity function and of the Halpha scaling relations down to ~ 10^6 Mo stellar mass objects, and the reconstruction of the dynamical structure of the Virgo cluster. This unique set of data will also be used to study the HII luminosity function in hundreds of galaxies, the diffuse Halpha+[NII] emission of the Milky Way at high Galactic latitude, and the properties of emission line galaxies at high redshift., Accepted for publication on Astronomy & Astrophysics