Determination Of Star Formation Rate Research Articles

STAR FORMATION RATE IN LATE-TYPE GALAXIES: I- THE Hα AND FUV INTEGRATED VALUES

The star formation rate (SFR) was determined from a sample of 36 late-type galaxies (14 dS and 22 Sm), from the SFR(H α ) and far ultraviolet (FUV) flux. We found that the SFR(FUV) is higher in most cases, larger for Sm galaxies and smaller for barred galaxies, for any morphological type, in both diagnostic methods. In addition, a study of the spatial distribution of star formation within these galaxies was made. We concluded that there is no preferential place for the star formation. Finally, we studied the role of the diffuse ionized gas in the SFR value; we found that the H α flux contribution from this gas should not be included in the SFR determination unless it is verified that leaking photons are the only source of the neutral gas ionization.

Prospects of the “WSO-UV” Project for Star Formation Study in Nearby Dwarf Galaxies

In the present work we consider the questions of star formation and evolution of nearby dwarf galaxies. We describe the method of star formation history determination based on multicolor photometry of resolved stars and models of color-magnitude diagrams of the galaxies. We present the results of star formation rate determination and its dependence on age and metallicity for dwarf irregular and dwarf spheroidal galaxies in the two nearby galaxy groups M81 and Cen A. Similar age of the last episode of star formation in the central part of the M81 group and also unusually high level of metal enrichment in the several galaxies of the Cen A group are mentioned. We pay special attention to the consideration of perspectives of star formation study in nearby dwarf galaxies with he new WSO-UV observatory.

A consistent view on star-forming galaxies at high redshift from multi-wavelength observations and SED modeling

AbstractWe stress the importance of consistent SED analysis for distant star-forming galaxies (SFGs). We then summarise recent results from such an analysis concerning their basic physical properties, such as the determination of star formation rate (SFR), stellar mass, specific star SFR, UV attenuation, and how this affects our knowledge of star formation properties at high-z.

Variations of the initial mass function in semi-analytical models

Deviations from a universal, MW-like, Stellar Initial Mass Function (IMF) have been reported for distant galaxies, although the physical reason behind the observed variations is still matter of ongoing debate. In this paper, we present an exploratory study to assess the impact of the proposed IMF evolution on the statistical galaxy properties, as predicted by the Semi-Analytical model of galaxy formation and evolution MORGANA. In particular, we test different dependencies for the IMF shape, as a function of both model galaxy properties (such as star formation rate, velocity dispersion or stellar mass) and environment, and compare the predicted stellar mass functions and star formation rate functions with reference runs at fixed IMF. In most cases, MORGANA predictions show deviations of the order of a few tenths of dex with respect to a run assuming an Universal Kroupa IMF. Among the proposed IMF variations, an increasing Top-Heavy IMF at increasing star formation rates has the largest impact on predicted galaxy properties, while most of the models assuming an increasing Bottom-Heavy IMF at higher masses/velocity dispersion lead to variations in galaxy properties that are of the same order as the uncertainty on the mass and star formation rate determination. By comparing the predicted galaxy stellar mass functions, we conclude that the study of the high-mass end can provide useful constraints to disentangle models assuming an increasing Top-Heavy IMF in high star forming or Bottom-Heavy IMF in massive systems.

DISCOVERY OF A LARGE POPULATION OF ULTRALUMINOUS X-RAY SOURCES IN THE BULGELESS GALAXIES NGC 337 AND ESO 501-23

We have used Chandra observations of eight bulge-less disk galaxies to identify new ultraluminous X-ray source (ULX) candidates, study their high mass X-ray binary (HMXB) population, and search for low-luminosity active galactic nuclei (AGN). We report the discovery of 16 new ULX candidates in our sample of galaxies. Eight of these are found in the star forming galaxy NGC 337, none of which are expected to be background contaminants. The HMXB luminosity function of NGC 337 implies a star formation rate (SFR) of 6.8$^{+4.4}_{-3.5}$ \msun\ yr$^{-1}$, consistent at 1.5$\sigma$ with a recent state of the art SFR determination. We also report the discovery of a bright ULX candidate (X-1) in ESO 501-23. X-1's spectrum is well fit by an absorbed power law with $\Gamma = 1.18^{+0.19}_{-0.11}$ and N$\rm{_H}$ = 1.13$^{+7.07}_{-1.13} \times 10^{20}$ cm$^{-2}$, implying a 0.3-8 keV flux of $1.08^{+0.05}_{-0.07} \times 10^{-12}$ \esc. Its X-ray luminosity (L$_X$) is poorly constrained due to uncertainties in the host galaxy's distance, but we argue that its spectrum implies L$_X > 10^{40}$ \es. An optical counterpart to this object may be present in HST imaging. We also identify ULX candidates in IC 1291, PGC 3853, NGC 5964 and NGC 2805. We find no evidence of nuclear activity in the galaxies in our sample, placing a flux upper limit of $4 \times 10^{-15}$ \esc\ on putative AGN. Additionally, the type II-P supernova SN 2011DQ in NGC 337, which exploded 2 months before our X-ray observation, is undetected.

The VVDS-SWIRE-GALEX-CFHTLS surveys: physical properties of galaxies at z below 1.2 from photometric data

Measuring the build-up of stellar mass is one of the main objectives of studies of galaxy evolution. Traditionally, the mass in stars and the star formation rates have been measured by different indicators, such as photometric colours, emission lines, and the UV and IR emission. We intend to show that it is possible to derive the physical parameters of galaxies from their broad-band spectral energy distribution out to a redshift of 1.2. This method has the potential to yield the physical parameters of all galaxies in a single field in a homogeneous way, thus overcoming problems with the sample size that particularly plague methods relying on spectroscopy. We use an extensive dataset, assembled in the context of the VVDS survey, which reaches from the UV to the IR and covers a sample of 84 073 galaxies over an area of 0.89 deg^2. We also use a library of 100 000 model galaxies with a wide variety of star formation histories (in particular including late bursts of star formation). We find that we can determine the physical parameters stellar mass, age, and star formation rate with good confidence. We validate the star formation rate determination in particular by comparing it to a sample of spectroscopically observed galaxies with an emission-line measurement. While the attenuation in the galaxies shows more scatter, the mean over the sample is unbiased. Metallicity, however, cannot be measured from rest-frame optical photometry alone. As a first application we use our sample to build the number density function of galaxies as a function of stellar mass, specific star formation rate, and redshift. We are then able to study whether the stellar mass function at a later time can be predicted from the stellar mass function and star formation rate distribution at an earlier time. We find that, between redshifts of 1.02 and 0.47, the predicted growth in stellar mass from star formation agrees with the observed one. However, the predicted stellar mass density for massive galaxies is lower than observed, while the mass density of intermediate mass galaxies is overpredicted. This apparent discrepancy can be explained by major and minor mergers. Indeed, when comparing with a direct measurement of the major merger rate from the VVDS survey, we find that major mergers can account for about half of the mass build-up at the massive end. Minor mergers are very likely to contribute the missing fraction. Based on data obtained with the European southern observatory Very Large Telescope, Paranal, Chile, programme 070A-9007(A) and on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS.

Investigations of star formation in galaxies using ALMA

ALMA provides unprecedented sensitivity and resolution to study gas and dust emission in the millimeter and submillimeter bands. The magnitude of the improvement is such that not only conventional studies can be done much better but entirely new tools and research fields should also become accessible. In this article, I examine several specific areas where new capabilities of ALMA will bring significant quantitative improvements to the determination of star formation rate and properties of the gas fueling the activities. I propose a survey of nearby galaxies with well measured metallicity gradient during the early phase of the ALMA operation as one of the key science projects.

Star Formation Rates in Interacting Starburst Galaxies

By narrowband imaging in Hα and in the adjacent red stellar continuum we have studied the rate and distribution of star formation in 43 systems of luminous and ultraluminous IR galaxies currently undergoing interaction and merging. These galaxies are amongst the most luminous at 60 μm and range in distance from ~50 up to 100 Mpc. Here we present the Hα and the adjacent red-continuum narrowband images, and we compare the star formation rates derived from Hα with those estimated from the IR luminosity. We find clear evidence for substantial extinction and obscuration of star-forming regions in the optical. Without correction for reddening in the host galaxy or correction for [N II] contamination, the star formation rates derived for Hα are typically 0.5-1.0 dex lower than those estimated from the IR flux, and the scatter in the correlation is very large. However, an unexpected result is that when spectroscopic data are used to eliminate objects dominated by an active nucleus, to determine the galaxian extinction, and to correct the Hα flux for both reddening and for the contamination by the [N II] emission, a remarkably good correlation emerges between the star formation rates estimated from the Hα flux and those derived from the FIR continuum. In addition, a strong correlation is found between the extinction in the line-emitting region, AHα, and the rate of star formation. Our results invalidate the use of Hα imaging as a reliable indicator of star formation in starburst galaxies unless spectroscopic data are also available. This has important implications for the determination of star formation rates in high-redshift galaxies. Finally, we find no correlation between the measured star formation rates, and the interaction class, suggesting that the enhanced star formation rates triggered by the interaction continue throughout the whole of the merging sequence.

On the Determination of Star Formation Rates in Evolving Galaxy Populations

The redshift dependence of the luminosity density in certain wave bands (e.g., UV and Hα) can be used to infer the history of star formation in the populations of galaxies producing this luminosity. This history is a useful datum in studies of galaxy evolution. It is therefore important to understand the errors that attend the inferring of star formation rate densities from luminosity densities. This paper explores the self-consistency of star formation rate diagnostics by reproducing commonly used observational procedures in a model with known galaxy populations, evolutionary histories, and spectral emission properties. The study reveals a number of potential sources of error in the diagnostic processes arising from the differential evolution of different galaxy types. We argue that multiwavelength observations can help to reduce these errors.