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1.
With the multi-wavelength data from UV to sub-millimeter in the region of H-ATLAS (Herschel Astrophysical Terahertz Large Area Survey) Science Demonstration Phase (SDP), in combination with the population synthesis model and dust model, the total infrared luminosities of the galaxies were calculated. On this basis, for respectively the strong and weak star-forming galaxies, we studied the differences in the star formation rates calculated by the UV luminosity, infrared luminosity and Hα line, as well as the intrinsic physical origin of such differences. It was found that for the galaxies of strong star-formation activity, the 3 kinds of star formation rate indicators give the basically consistent results with a small dispersion. But at the end of high star formation rate, the star formation rate calculated by the UV luminosity is slightly smaller than that calculated by the Hα-line flux; at the end of low star formation rate, the UV indicator tends to be greater than the Hα indicator; and at both ends, the infrared indicator and Hα indicator have no significant difference. For the weak star-forming galaxies, significant differences exist among the 3 kinds of indicators, and there is a rather large dispersion. The dispersions and systematic difference of the star formation rates calculated by the UV luminosity and Hα line increase with the galactic age and mass. The main cause for the increased systematic difference is that when the extinction of an weak star-forming galaxy is calibrated by its UV continuum spectral slope β, the UV extinction of the galaxy is overestimated, it makes the UV luminosity tends to be large after the extinction correction. In addition, the star formation rates (Hα) of weak starforming galaxies in the MPA/JHU (Max Planck Institute for Astrophysics/Johns Hopkins University) database are generally less than the real values.  相似文献   

2.
We present the first results of our Hubble Space Telescope HST WFPC2 F814W snapshot imaging survey, targeting virtually all sub-mJy decimetric radio-selected star-forming galaxies. The radio selection at ∼1 GHz is free from extinction effects and the radio luminosities are largely unaffected by AGN contamination, making these galaxies ideal tracers of the cosmic star formation history. A subsample of four targets is presented here, selected at 1.4 GHz from the spectroscopically homogenous and complete samples of Benn et al. and Hopkins et al. The redshifts are confined to a narrow range around z ∼0.2, to avoid differential evolution, with a radio luminosity close to L ∗ where the galaxies dominate the comoving volume-averaged star formation rate. We find clearly disturbed morphologies resembling those of ultraluminous infrared galaxies, indicating that galaxy interactions may be the dominant mechanism for triggering star formation at these epochs. The morphologies are also clearly different from those of coeval quasars and radio galaxies, as found in star-forming galaxies selected at other wavelengths. This may prove challenging for models that propose direct causal links between AGN evolution and the cosmic star formation history at these epochs. The asymmetries are typically much larger than seen in the Canada–France Redshift Survey at similar redshifts, optical luminosities and H α -derived star formation rates, indicating the possible existence of an obscuration-related morphological bias in such samples.  相似文献   

3.
The Phoenix Deep Survey is an ongoing multi-wavelength survey of a 2° diameter field aimed at studying the properties of the sub-mJy and μJy radio population. Here, we present the latest 1.4 GHz observations of this field. The new data, reaching a 5 σ flux level of 45 μJy at the centre of a 50′ diameter field, comprise more than 700 sources with flux densities less than 1 mJy (187 of which have S1.4 < 100 μJy). This provides one of the deepest radio (1.4 GHz) surveys currently available. The 1.4 GHz source counts are presented and show a flattening down to the 50 μJy level. At flux densities around 300 μJy there are indications that the sources detected may exhibit higher clustering than those observed at higher flux levels. This suggests that deep radio surveys could be useful for studies of large-scale structure but it also presents a warning for the representativity of sources in deep pencil-beam radio surveys. The study of the optical counterparts of the μJy population seems to indicate that the median R magnitude starts to decrease below 100 μJy. Spectroscopic classification of a sample of sources in this survey confirms the trend for an increasing fraction of star-forming galaxies over other systems down to ～ 100 μJy.  相似文献   

4.
《New Astronomy Reviews》2002,46(2-7):203-205
With objectives to model star formation in radio galaxies, we present results of a starburst model, built by coupling the two codes PÉGASE and CLOUDY. Continuum and emission line data are used to derive the properties of a sample of local starbursts. Data are well reproduced with a new relation between the ionization parameter and the metallicity. Colors and Hα equivalent widths indicate that: (i) an underlying stellar population is needed, and (ii) burst ages span the range [0, 6] Myr.  相似文献   

5.
We present the results of a statistical study of the star formation rates (SFR) derived from the Galaxy Evolution Explorer (GALEX) observations in the ultraviolet continuum and in the Hα emission line for a sample of about 800 luminous compact galaxies (LCGs). Galaxies in this sample have a compact structure and include one or several regions of active star formation. Global galaxy characteristics (metallicity, luminosity, stellar mass) are intermediate between ones of the nearby blue compact dwarf (BCD) galaxies and Lyman-break galaxies (LBGs) at high redshifts z>2–3. SFRs were corrected for interstellar extinction which was derived from the optical Sloan Digital Sky Survey (SDSS) spectra. We find that SFRs derived from the galaxy luminosities in the far ultraviolet (FUV) and near ultraviolet (NUV) ranges vary in a wide range from 0.18 M ⊙?yr?1 to 113 M ⊙?yr?1 with median values of 3.8 M ⊙?yr?1 and 5.2 M ⊙?yr?1, respectively. Simple regression relations are found for luminosities L(Hα) and L(UV) as functions of the mass of the young stellar population, the starburst age, and the galaxy metallicity. We consider the evolution of L(Hα), L(FUV) and L(NUV) with a starburst age and introduce new characteristics of star formation, namely the initial Hα, FUV and NUV luminosities at zero starburst age.  相似文献   

6.
The Lyα line is an important diagnostic of star formation and activity in galaxies. The analysis of Lyα is complicated due to the resonant nature of the line and radiative transfer effects. High spectral resolution studies of local starburst galaxies with the unprecedented UV capabilities of the HST have shown that this line is either seen in absorption or in emission and in the latter case with a P?Cygni profile indicative of a large scale outflow of neutral gas. Moreover, HST imaging obtained with HST-ACS of a sample of 6 star-forming galaxies has revealed that a substantial fraction of the Lyα photons are diffused far away from the emissive knots. Since the importance of Lyα for tracing large scale structure, correlation functions, and galaxy formation is recognized, Lyα will remain a very important probe of the distant universe for the foreseeable future, and it is therefore imperative to acquire a better understanding of what mechanisms regulate our ability to detect this line.  相似文献   

7.
We probe the relationship between star formation rate (SFR) and radio synchrotron luminosity in galaxies at  0 < z < 2  within the northern Spitzer Wide-area Infrared Extragalactic survey (SWIRE) fields, in order to investigate some of the assumptions that go into calculating the star formation history of the Universe from deep radio observations. We present new 610-MHz Giant Metrewave Radio Telescope (GMRT) observations of the European Large-Area ISO Survey-North 2 (ELAIS-N2) field, and using this data, along with previous GMRT surveys carried out in the ELAIS-N1 (North 1) and Lockman Hole regions, we construct a sample of galaxies which have redshift and SFR information available from the SWIRE survey. We test whether the local relationship between SFR and radio luminosity is applicable to   z = 2  galaxies, and look for evolution in this relationship with both redshift and SFR in order to examine whether the physical processes which lead to synchrotron radiation have remained the same since the peak of star formation in the Universe. We find that the local calibration between radio luminosity and star formation can be successfully applied to radio-selected high-redshift, high-SFR galaxies, although we identify a small number of sources where this may not be the case; these sources show evidence for inaccurate estimations of their SFR, but there may also be some contribution from physical effects such as the recent onset of starburst activity, or suppression of the radio luminosity within these galaxies.  相似文献   

8.
We have cross-matched the 1.4-GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325 deg2 (about 20 per cent of the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio identifications – the largest and most homogeneous set of radio source spectra ever obtained. The 2dFGRS radio sources span the redshift range     to 0.438, and are a mixture of active galaxies (60 per cent) and star-forming galaxies (40 per cent). About 25 per cent of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1 Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star-forming galaxies. We make a new determination of the local radio luminosity function at 1.4 GHz for both active and star-forming galaxies, and derive a local star formation density of         .  相似文献   

9.
Luminous infrared galaxies (LIRGs) provide insights into star formation (SF) and nuclear activity (AGN) under extreme conditions. We are carrying out a multi-wavelength (X-rays, ultraviolet through mid-infrared, and radio) program to obtain high angular resolution observations of a volume-limited sample of local LIRGs. The typical distances to these LIRGs (D=35–75 Mpc) allow us to identify star clusters and H II regions on scales of tens to hundreds of parsecs. We present here recent results on properties of the massive star-forming regions and star clusters in two LIRGs in our sample, Arp 299 and NGC7469.  相似文献   

10.
For a sample of 8156 emission-line galaxies from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4), we have determined the current star formation rates (SFR) from three parameters: the Hα luminosity of H II regions corrected for the aperture and interstellar extinction (N = 7006 galaxies), the far-infrared luminosity (IRAS data, N = 350), and the monochromatic luminosity in the radio continuum at ν = 1.4 GHz (NVSS data, N = 475). A Salpeter initial mass function with the range of stellar masses 0.1–100 M ⊙ was assumed in the SFR FIR calculations. In calculating SFR1.4, we assumed that the fraction of the thermal emission in the total radio continuum emission of the galaxy at 1.4 GHz was 10%. An upper limit for the starburst age has been determined for galaxies with known abundances of heavy elements. We compare our results with those of similar studies for isolated and Markarian H II galaxies.  相似文献   

11.
We present the first results of an ongoing spectroscopic survey of galaxies selected in the rest frame ultraviolet (UV). The source catalogue has been constructed from a flux-limited sample of stars, galaxies and QSOs imaged at 2000 Å in Selected Area 57 with the FOCA balloon-borne imaging camera. Accurate positions for the UV sources have been obtained by matching with optical counterparts using APM scans of the Palomar Sky Survey limited at B   20.5. Here we present results derived from optical spectroscopy conducted with the WIYN telescope and the WHT for 142 faint sources. The redshift distribution for this UV-selected sample extends over 0 <  z  < 0.5, and a high fraction of the sources show intense nebular emission lines and UV–optical colours bluer than normal Hubble sequence galaxies. Such UV-selected surveys are thus a very efficient way to locate and study intermediate-redshift galaxies undergoing intense star formation. Although our sample is currently small, we derive a rest frame UV luminosity function with a steep faint-end slope consistent with that found for late-type galaxies in optical samples. However, the integrated luminosity density derived implies a volume-averaged star formation rate higher than other recent estimates, assuming a normal initial mass function. If representative of other UV fields, as suggested by UV number count studies, our data imply that the local abundance of star-forming galaxies may have been underestimated, and consequently claims for strong evolution in the global star formation rate in the range 0 <  z  < 1 overstated. An intensive study of a large UV-selected sample is likely to reveal important information on the declining population of star-forming galaxies of all types.  相似文献   

12.
We summarize our modelling of galaxy photometric evolution (the GRASIL code). By including the effects of dust grains and PAH molecules in a two-phase clumpy medium, where clumps are associated with star-forming regions, we reproduce the observed UV to radio SEDs of galaxies with star formation rates from zero to several hundred M ⊙ yr-1.GRASIL is a powerful tool for investigating star formation, the initial mass function and the supernova rate in nearby starbursts and normal galaxies, as well as for predicting the evolution of luminosity functions of different types of galaxies at wavelengths covering six decades. It may be interfaced with any device to provide the star formation and metallicity histories of a galaxy. As an application, we have investigated the properties of early-type galaxies in the HDF, tracking the contribution of this population to the cosmic star formation history, which has a broad peak between z = 1.5 and 4.To explain the absence of objects at z ≳ 1.3, we suggest a sequence of dust-enshrouded merger-driven starbursts in the first few Gyr of galaxy lifetimes. We are at present working on a complementary sample of late-type objects selected in a similar way. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

13.
《New Astronomy Reviews》2000,44(4-6):283-285
The statistical investigation of integrated characteristics of the blue compact galaxies from the Second Byurakan survey has been carried out. The tight correlation between the luminosities in the far-infrared range and radio range (radio-continuum at 21 cm) has been revealed. It implies the common origin of this radiation in star forming regions. The current star formation rates have been derived both from the luminosity in the far-infrared range (SFRFIR) and from the luminosity in the radio range (SFR21 cm). The Salpeter shape of the initial mass function (IMF) and low-mass cut-off of 0.1 M⊙ in IMF has been assumed for the SFRFIR calculation. We derive the SFR21 cm assuming that radio free–free emission at λ=21 cm is thermal emission of gas ionised by massive stars. The SFR21 cm is shown to be about 3.5 times as large as SFRFIR for our sample of galaxies. These star formation rates are proposed to be considered as lower and upper limits of true galaxy star formation rates.  相似文献   

14.
We present our Hα observations of 11 isolated southern galaxies: SDIG, PGC 51659, E 222-010, E 272-025, E 137-018, IC 4662, Sag DIG, IC 5052, IC 5152, UGCA 438, and E 149-003, with distances from 1 to 7 Mpc. We have determined the total Hα fluxes from these galaxies. The star formation rates in these galaxies range from 10?1 (IC 4662) to 10?4 M ⊙ yr?1 (SDIG) and the gas depletion time at the observed star formation rates lies within the range from 1/6 to 24 Hubble times H 0 ?1 .  相似文献   

15.
We analyze the statistical properties of normal galaxies to be detected in the all-sky survey by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory. With the current configuration and parameters of the eROSITA telescope, the sensitivity of a 4-year-long all-sky survey will be ≈10?14 erg s?1 in the 0.5–2 keV band. This will allow ～(1.5–2) × 104 normal galaxies with approximately the same contribution of star-forming and elliptical galaxies to be detected. All galaxies of the X-ray survey are expected to enter into the existing far-infrared (IRAS) or near-infrared (2MASS) catalogs; the sample of star-forming galaxies will be approximately equivalent in sensitivity to the sample of star-forming galaxies in the IRAS catalog of infrared sources. Thus, a large homogeneous sample of normal galaxies with measured X-ray, near-infrared, and far-infrared fluxes will be formed. About 90% of the galaxies in the survey are located within ～200–400 Mpc. A typical (most probable) galaxy will have a luminosity log L X ～ 40.5–41.0, will be located at a distance of ～70–90 Mpc, and will be either a star-forming galaxy with a star formation rate of ～20M ⊙ yr?1 whose X-ray emission is produced by ultraluminous X-ray sources (ULXs) or an elliptical galaxy with amass log M * ～ 11.3 emitting through to a hot interstellar gas. The galaxies within 35 Mpc will collectively contain ～102 ULXs with luminosities log L X > 40, ～80% of whichwill be the only luminous source in the galaxy. Thus, although the angular resolution of the eROSITA telescope is too low for the luminosity function of compact sources in galaxies to be studied in detail, the survey data will allow one to investigate its bright end and, possibly, to impose constraints on the maximum luminosity of ULXs.  相似文献   

16.
We examine the evolutionary status of luminous, star-forming galaxies in intermediate-redshift clusters by considering their star formation rates (SFRs) and the chemical and ionization properties of their interstellar emitting gas. Our sample consists of 17 massive, star-forming, mostly disc galaxies with   MB ≲−20  , in clusters with redshifts in the range  0.31 ≲ z ≲ 0.59  , with a median of  〈 z 〉= 0.42  . We compare these galaxies with the identically selected and analysed intermediate-redshift field sample of Mouhcine et al., and with local galaxies from the Nearby Field Galaxy Survey of Jansen et al.
From our optical spectra, we measure the equivalent widths of  [O  ii ]λ3727, Hβ  and [O  iii ]λ5007 emission lines to determine diagnostic line ratios, oxygen abundances and extinction-corrected SFRs. The star-forming galaxies in intermediate-redshift clusters display emission-line equivalent widths which are, on average, significantly smaller than measured for field galaxies at comparable redshifts. However, a contrasting fraction of our cluster galaxies have equivalent widths similar to the highest observed in the field. This tentatively suggests a bimodality in the SFRs per unit luminosity for galaxies in distant clusters. We find no evidence for further bimodalities, or differences between our cluster and field samples, when examining additional diagnostics and the oxygen abundances of our galaxies. This maybe because no such differences exist, perhaps because the cluster galaxies which still display signs of star formation have recently arrived from the field. In order to examine this topic with more certainty, and to further investigate the way in which any disparity varies as a function of cluster properties, larger spectroscopic samples are needed.  相似文献   

17.
With the goal of investigating the degree at which the MIR luminosity in the Wide-field Infrared Survey Explorer (WISE) traces the SFR, we analyse 3.4, 4.6, 12 and 22 ??m data in a sample of ~140,000 star-forming galaxies or star-forming regions covering a wide range in metallicity 7.66 < 12 + log(O/H)<9.46, with redshift z?< 0.4. These star-forming galaxies or star-forming regions are selected by matching the WISE Preliminary Release Catalog with the star-forming galaxy Catalog in SDSS DR8 provided by JHU/MPA1?. We study the relationship between the luminosity at 3.4, 4.6, 12 and 22 ??m from WISE and H?? luminosity in SDSS DR8. From these comparisons, we derive reference SFR indicators for use in our analysis. Linear correlations between SFR and the 3.4, 4.6, 12 and 22 ??m luminosity are found, and calibrations of SFRs based on L(3.4), L(4.6), L(12) and L(22) are proposed. The calibrations hold for galaxies with verified spectral observations. The dispersion in the relation between 3.4, 4.6, 12 and 22 ??m luminosity and SFR relates to the galaxy??s properties, such as 4000 ? break and galaxy color.  相似文献   

18.
We present new near-infrared J and K imaging data for 67 galaxies from the Universidad Complutense de Madrid (UCM) survey used in the determination of the SFR density of the local Universe by Gallego et al. This is a sample of local star-forming galaxies with redshift lower than 0.045, and they constitute a representative subsample of the galaxies in the complete UCM survey. From the new data, complemented with our own Gunn- r images and long-slit optical spectroscopy, we have measured integrated K -band luminosities, r − J and J − K colours, and H α luminosities and equivalent widths. Using a maximum likelihood estimator and a complete set of evolutionary synthesis models, these observations allow us to estimate the strength of the current (or most recent) burst of star formation, its age, the star formation rate and the total stellar mass of the galaxies. An average galaxy in the sample has a stellar mass of 5×1010 M⊙ and is undergoing (or has recently completed) a burst of star formation involving about 2 per cent of its total stellar mass. We identify two separate classes of star-forming galaxies in the UCM sample: low-luminosity, high-excitation galaxies (H  ii like ) and relatively luminous spiral galaxies (starburst disc- like ). The former show higher specific star formation rates (SFRs per unit mass) and burst strengths, and lower stellar masses than the latter. With regard to their specific star formation rates, the UCM galaxies are intermediate objects between normal quiescent spirals and the most extreme H  ii galaxies.  相似文献   

19.
The significance of tidal interactions in the evolution of the faint radio population (sub-mJy) is studied using a deep and homogeneous radio survey (1.4 GHz), covering an area of 3.14 deg2 and complete to a flux density of 0.4 mJy. Optical photometric and spectroscopic data are also available for this sample. A statistical approach is employed to identify candidate physical associations between radio sources and optically selected 'field' galaxies. We find an excess of close pairs around optically identified faint radio sources, albeit at a low significance level, implying that the pairing fraction of the sub-mJy radio sources is similar to that of 'field' galaxies (at the same magnitude limit) but higher than that of local galaxies.  相似文献   

20.
The existence or otherwise of X-ray luminous star-forming galaxies has been an open question since the era of the Einstein satellite. Various authors have claimed the discovery of X-ray luminous star-forming galaxies but in many cases more careful spectroscopic studies of these objects have shown that many of them are in fact obscured AGN. In order to investigate the possibility that such a class of galaxies do exist, we have carried out a cross-correlation between optical and IRAS samples of galaxies which are known to contain large numbers of star-forming galaxies and catalogues of sources detected in X-ray surveys. The selection criteria for the optical follow-up observations was based on their X-ray and infrared (IRAS) colours and their X-ray luminosities. We note that this sample is by no means complete or uniformly selected and hence cannot be used for statistical studies; nevertheless, confirmation of the existence of such a class of objects would be an important step and would require us to understand the physical process responsible for such powerful X-ray emission. We have initiated an optical spectroscopic survey in order to obtain accurate spectroscopic classifications for all the objects which are claimed to be starburst galaxies. Here we present preliminary results from this survey. We have discovered a number of starburst galaxies with X-ray luminosities above ～ 1041 erg s-1 (for H 0=50 km s-1 Mpc-1).We investigate possible origins for the X-ray emission in individual cases.  相似文献   

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