We present an overview of the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). STAGES is a multiwavelength project designed to probe physical drivers of galaxy evolution across a wide range of environments and luminosity. A complex multicluster system at z~0.165 has been the subject of an 80-orbit F606W Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) mosaic covering the full 0.5x0.5deg^2^ (~5x5Mpc^2^) span of the supercluster. Extensive multiwavelength observations with XMM-Newton, GALEX, Spitzer, 2dF, Giant Metrewave Radio Telescope and the 17-band COMBO-17 photometric redshift survey complement the HST imaging. Our survey goals include simultaneously linking galaxy morphology with other observables such as age, star formation rate, nuclear activity and stellar mass. In addition, with the multiwavelength data set and new high-resolution mass maps from gravitational lensing, we are able to disentangle the large-scale structure of the system. By examining all aspects of an environment we will be able to evaluate the relative importance of the dark matter haloes, the local galaxy density and the hot X-ray gas in driving galaxy transformation.
We present a multi-wavelength compilation of new and previously published photometry for 55 Galactic field RR Lyrae variables. Individual studies, spanning a time baseline of up to 30 years, are self-consistently phased to produce light curves in 10 photometric bands covering the wavelength range from 0.4 to 4.5 microns. Data smoothing via the GLOESS technique is described and applied to generate high-fidelity light curves, from which mean magnitudes, amplitudes, rise times, and times of minimum and maximum light are derived. 60000 observations were acquired using the new robotic Three-hundred MilliMeter Telescope (TMMT), which was first deployed at the Carnegie Observatories in Pasadena, CA, and is now permanently installed and operating at Las Campanas Observatory in Chile. We provide a full description of the TMMT hardware, software, and data reduction pipeline. Archival photometry contributed approximately 31000 observations. Photometric data are given in the standard Johnson UBV, Kron-Cousins R_C_I_C_, 2MASS JHK, and Spitzer [3.6] and [4.5] bandpasses.
A single table combines the revised and extended results of 24 series of photometric observations made in South Africa between 1947 and 1960 on the nine Harvard E regions at declination -45{deg}. For each of about 90 stars in each region are tabulated V and B-V on the standard U,B,V system, an ultraviolet-free blue magnitude S'Pg, a photovisual magnitude SPv and, in most cases, an ultraviolet minus blue colour (U-B)_C_. The internal standard error of an entry is +/-0.01mag or less.
We have combined near-infrared data from the Two Micron All Sky Survey with ancillary optical data to identify previously unrecognized proper-motion stars that have colors and magnitudes consistent with nearby M dwarfs. We present follow-up observations of 392 stars from that sample, including ~200 stars discussed here for the first time. Our distance estimates, based primarily on spectroscopic parallaxes, place 123 stars within 20pc of the Sun. One hundred and seventy-six stars exhibit H{alpha} emission, and 82 stars have plausible X-ray counterparts from ROSAT observations.
At high redshift, starburst galaxies present irregular morphologies, with 10-20% of their star formation occurring in giant clumps. These clumpy galaxies are considered to be the progenitors of local disk galaxies. To understand the properties of starbursts at intermediate and low redshift, it is fundamental to track their evolution and possible link with the systems at higher z. We present an extensive, systematic, and multi-band search and analysis of the starburst galaxies at redshift (0<z<0.5) in the COSMOS field, as well as detailed characteristics of their star-forming clumps by using Hubble Space Telescope/Advance Camera for Surveys (HST/ACS) images. The starburst galaxies are identified using a tailor-made intermediate-band color excess selection, tracing the simultaneous presence of H{alpha} and [OIII] emission lines in the galaxies. Our methodology uses previous information from the zCOSMOS spectral database to calibrate the color excess as a function of the equivalent width of both spectral lines. This technique allows us to identify 220 starburst galaxies at redshift 0<z<0.5 using the SUBARU intermediate-band filters. Combining the high spatial resolution images from the HST/ACS with ground-based multi-wavelength photometry we identify and parametrize the star-forming clumps in every galaxy. Their principal properties, sizes, masses, and star formation rates are provided.
A summary of starburst luminosities based on polycyclic aromatic hydrocarbon (PAH) features is given for 243 starburst galaxies with 0<z<2.5, observed with the Spitzer Infrared Spectrograph. Luminosity {nu}L_{nu}_(7.7um) for the peak luminosity of the 7.7um PAH emission feature is found to scale as log[{nu}L_{nu}_(7.7{mu}m)]=44.63(+/-0.09)+2.48(+/-0.28)log(1+z) for the most luminous starbursts observed. Empirical calibrations of {nu}L_{nu}_(7.7um) are used to determine bolometric luminosity L_IR_ and the star formation rate (SFR) for these starbursts. The most luminous starbursts found in this sample have logL_IR_=45.4(+/-0.3)+2.5(+/-0.3)log(1+z), in ergs/s, and the maximum star formation rates for starbursts in units of M_{sun}_/yr are log(SFR)=2.1(+/-0.3)+2.5(+/-0.3)log(1+z), up to z=2.5. The exponent for pure luminosity evolution agrees with optical and radio studies of starbursts but is flatter than previous results based in infrared source counts. The maximum star formation rates are similar to the maxima determined for submillimeter galaxies; the most luminous individual starburst included within the sample has logL_IR_=46.9, which gives an SFR=3.4x10^3^M_{sun}/yr. Description: In this paper, we assemble data from 14 different Spitzer/IRS (InfraRed Spectrograph) programs (listed in "Ref" column of table1) to summarize a wide variety of sources having strong PAH spectral features, providing a total of 243 sources.
StarCAT is a catalog of high resolution ultraviolet spectra of objects classified as "stars," recorded by Space Telescope Imaging Spectrograph (STIS) during its initial seven years of operations (1997-2004). StarCAT is based on 3184 echelle observations of 545 distinct targets, with a total exposure duration of 5.2Ms. For many of the objects, broad ultraviolet coverage has been achieved by splicing echellegrams taken in two or more FUV (1150-1700{AA}) and/or NUV (1600-3100{AA}) settings. In cases of multiple pointings on conspicuously variable sources, spectra were separated into independent epochs. Otherwise, different epochs were combined to enhance the signal-to-noise ratio (S/N). A post-facto correction to the "calstis" pipeline data sets compensated for subtle wavelength distortions identified in a previous study of the STIS calibration lamps. An internal "fluxing" procedure yielded coherent spectral energy distributions (SEDs) for objects with broadly overlapping wavelength coverage. The best StarCAT material achieves 300m/s internal velocity precision; absolute accuracy at the 1km/s level; photometric accuracy of order 4%; and relative flux precision several times better (limited mainly by knowledge of SEDs of UV standard stars). While StarCAT represents a milestone in the large-scale post-processing of STIS echellegrams, a number of potential improvements in the underlying "final" pipeline are identified.
The formation of globular clusters remains an open debate. Dwarf starburst galaxies are efficient at forming young massive clusters with similar masses as globular clusters and may hold the key to understanding their formation. We study star cluster formation in a tidal debris - including the vicinity of three tidal dwarf galaxies - in a massive gas dominated collisional ring around NGC 5291. These dwarfs have physical parameters which differ significantly from local starbursting dwarfs. They are gas-rich, highly turbulent, have a gas metallicity already enriched up to half-solar, and are expected to be free of dark matter. The aim is to study massive star cluster formation in this as yet unexplored type of environment. We use imaging from the Hubble Space Telescope using broadband filters covering the wavelength range from the near- ultraviolet to the near-infrared. We determine the masses and ages of the cluster candidates by using the spectral energy distribution- fitting code CIGALE, carefully considering age-extinction degeneracy effects on the estimation of the physical parameters. Results. We find that the tidal dwarf galaxies in the ring of NGC 5291 are forming star clusters with an average efficiency of about 40%, comparable to blue compact dwarf galaxies. We also find massive star clusters for which the photometry suggests that they were formed at the very birth of the tidal dwarf galaxies and have survived for several hundred million years. Therefore our study shows that extended tidal dwarf galaxies and compact clusters may be formed simultaneously. In the specific case observed here, the young star clusters are not massive enough to survive for a Hubble time. However one may speculate that similar objects at higher redshift, with higher star formation rate, might form some of the long lived globular clusters.
Aims: Our goal is to investigate the formation of star clusters in relatively unperturbed environments. To do this, we studied the five nearby spiral galaxies: NGC 45, NGC 1313, NGC 4395, NGC 5236, and NGC 7793. Methods: We obtained images of the galaxies and their star cluster systems in UBVI using the Advanced Camera for Surveys (ACS) and the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope. From a comparison of the broad-band colours with simple stellar population (SSP) models, we derived individual properties for each galaxy for the clusters such such as masses, ages, and sizes, as well as global star cluster system properties such as the age distribution, luminosity function, and disruption time for clusters. Results. We identified about 600 star cluster candidates in the five galaxies, typically spanning ages from 3.9Myr up to 1Gyr and masses from 10^2^M_{sun}_ up to 10^5^M_{sun}_. We used the cluster age distribution to reconstruct the recent star formation history of each galaxy and observed significant variations from galaxy to galaxy. We went on to derive the luminosity function of the young star clusters and found slopes around {alpha}~-2 (similar to the ones found in previous studies) and the brightest star cluster magnitudes consistent with a random sampling of the luminosity function without involving an upper luminosity cut off. Finally, the sample includes only a handful of old globular clusters in each galaxy from which we derive low globular cluster specific frequencies.
In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC) in order to provide their mean metallicities and ages. We also provide mean metallicities of the fields surrounding the clusters. We used Stroemgren photometry obtained with the 4.1 m SOAR telescope and take advantage of (b-y) and m1 colors for which there is a metallicity calibration presented in the literature. The spatial metallicity and age distributions of clusters across the SMC are investigated using the results obtained by Stroemgren photometry. We confirm earlier observations that younger, more metal-rich star clusters are concentrated in the central regions of the galaxy, while older, more metal-poor clusters are located farther from the SMC center. We construct the age-metallicity relation for the studied clusters and find good agreement with theoretical models of chemical enrichment, and with other literature age and metallicity values for those clusters. We also provide the mean metallicities for old and young populations of the field stars surrounding the clusters, and find the latter to be in good agreement with recent studies of the SMC Cepheid population. Finally, the Stroemgren photometry obtained for this study is made publicly available.
