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Star-forming Galaxies (star-forming + galaxy)
Selected AbstractsRed star-forming and blue passive galaxies in clustersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009Smriti Mahajan ABSTRACT We explore the relation between colour (measured from photometry) and specific star formation rate (derived from optical spectra obtained by the Sloan Digital Sky Survey Data Release 4) of over 6000 galaxies (Mr,,20.5) in and around (<3 r200) low-redshift (z < 0.12) Abell clusters. Even though, as expected, most red sequence galaxies have little or no ongoing star formation, and most blue galaxies are currently forming stars, there are significant populations of red star-forming and blue passive galaxies. This paper examines various properties of galaxies belonging to the latter two categories, to understand why they deviate from the norm. These properties include morphological parameters, internal extinction, spectral features such as EW(H,) and the 4000 Å break, and metallicity. Our analysis shows that the blue passive galaxies have properties very similar to their star-forming counterparts, except that their large range in H, equivalent width indicates recent truncation of star formation. The red star-forming galaxies fall into two broad categories, one of them being massive galaxies in cluster cores dominated by an old stellar population, but with evidence of current star formation in the core (possibly linked with active galactic nuclei). For the remaining red star-forming galaxies, it is evident from spectral indices, stellar and gas-phase metallicities and mean stellar ages that their colours result from the predominance of a metal-rich stellar population. Only half of the red star-forming galaxies have extinction values consistent with a significant presence of dust. The implication of the properties of these star-forming galaxies on environmental studies, like that of the Butcher,Oemler effect, is discussed. [source] IRAC photometric analysis and the mid-IR photometric properties of Lyman-break galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008G. E. Magdis ABSTRACT We present photometric analysis of deep mid-infrared (mid-IR) observations obtained by Spitzer/IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 751 Lyman-break galaxies (LBGs) lying in those fields, 443, 448, 137 and 152 are identified at 3.6-, 4.5-, 5.8-, 8.0-,m IRAC bands, respectively, expanding their spectral energy distribution to rest-near-IR and revealing that LBGs display a variety of colours. Their rest-near-IR properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit [R],[3.6] > 1.5 colours to those that are faint or not detected at all in IRAC bands with [R],[3.6] < 1.5 colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-forming galaxies at z, 3. The properties of the LBGs detected in the 8-,m IRAC band (rest-frame K band) are examined separately, showing that they exhibit redder [R],[3.6] colours than the rest of the population and that although in general, a multiwavelength study is needed to reach more secure results, IRAC 8-,m band can be used as a diagnostic tool, to separate high z, luminous AGN-dominated objects from normal star-forming galaxies at z, 3. [source] The evolution of submillimetre galaxies: two populations and a redshift cut-offMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008J. V. Wall ABSTRACT We explore the epoch dependence of number density and star formation rate for submillimetre galaxies (SMGs) found at 850 ,m. The study uses a sample of 38 SMG in the Great Observatories Origins Deep Survey (GOODS)-N field, for which cross-waveband identifications have been obtained for 35/38 members together with redshift measurements or estimates. A maximum-likelihood analysis is employed, along with the ,single-source-survey' technique. We find a diminution in both space-density and star formation rate at z > 3, closely mimicking the redshift cut-offs found for quasi-stellar objects (QSOs) selected in different wavebands. The diminution in redshift is particularly marked at a significance level too small to measure. The data further suggest, at a significance level of about 0.001, that two separately evolving populations may be present, with distinct luminosity functions. These results parallel the different evolutionary behaviours of Luminous Infrared Galaxies and Ultra-Luminous Infrared Galaxies, and represent another manifestation of ,cosmic down-sizing', suggesting that differential evolution extends to the most extreme star-forming galaxies. [source] Environments of z > 5 quasars: searching for protoclusters at submillimetre wavelengthsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008R. S. Priddey ABSTRACT We present submillimetre (submm) continuum images of the fields of three luminous quasars at z > 5, obtained at 850 and 450 ,m using the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope (JCMT). N -body simulations predict that such quasars evolve to become the central dominant galaxies of massive clusters at z= 0, but at z= 5,6 they are actively forming stars and surrounded by a rich protofilamentary structure of young galaxies. Our purpose in taking these images was to search for other luminous, star-forming galaxies in the vicinity of the signpost active galactic nuclei and thus associated with such a protocluster. Two of the quasar host galaxies are luminous submm galaxies (SMGs) in their own right, implying star formation rates ,103 M, yr,1. Despite the coarse 850-,m beam of the JCMT, our images show evidence of extended emission on a scale of ,100 kpc from at least one quasar , indicative of a partially resolved merger or a colossal host galaxy. In addition, at >3, significance we detect 12 (5) SMGs at 850 ,m (450 ,m) in the surrounding fields. Number counts of these SMGs are comparable with those detected in the fields of z, 4 radio galaxies, and both samples are, at the bright end, overabundant by a factor of ,4 relative to blank-field submm surveys. Whilst the redshift-sensitive 850 ,m/450 ,m and 850 ,m/1.4 GHz flux density ratios indicate that some of these SMGs are likely foreground objects, the counts suggest that ,60 per cent lie in the same large-scale structures as the quasars. [source] The stellar mass density at z, 6 from Spitzer imaging of i,-drop galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007Laurence P. Eyles ABSTRACT We measure the ages, stellar masses, and star formation histories of z, 6 galaxies, observed within 1 Gyr of the big bang. We use imaging from the Hubble Space Telescope (HST) and the Spitzer Space Telescope from the public ,Great Observatories Origins Deep Survey' (GOODS), coupled with ground-based near-infrared imaging, to measure their spectral energy distributions (SEDs) from 0.8,5 ,m, spanning the rest-frame ultraviolet (UV) and optical. From our sample of ,50 ,i,-drop' Lyman-break star-forming galaxies in GOODS-South with z,AB < 27, we focus on ,30 with reliable photometric or spectroscopic redshifts. Half of these are confused with foreground sources at Spitzer resolution, but from the 16 with clean photometry we find that a surprisingly large fraction (40 per cent) have evidence for substantial Balmer/4000-Å spectral breaks. This indicates the presence of old underlying stellar populations that dominate the stellar masses. For these objects, we find ages of ,200,700 Myr, implying formation redshifts of 7 ,zf, 18, and large stellar masses in the range ,1,3 × 1010 M,. Analysis of seven i,-drops that are undetected at 3.6 ,m indicates that these are younger, considerably less massive systems. We calculate that emission line contamination should not severely affect our photometry or derived results. Using SED fits out to 8 ,m, we find little evidence for substantial intrinsic dust reddening in our sources. We use our individual galaxy results to obtain an estimate of the global stellar mass density at z, 6. Correcting for incompleteness in our sample, we find the z, 6 comoving stellar mass density to be 2.5 × 106 M, Mpc,3. This is a lower limit, as post-starburst and dust-obscured objects, and also galaxies below our selection thresholds, are not accounted for. From our results, we are able to explore the star formation histories of our selected galaxies, and we suggest that the past global star formation rate may have been much higher than that observed at the z, 6 epoch. The associated UV flux we infer at z > 7 could have played a major role in reionizing the Universe. [source] Lyman break galaxies and the star formation rate of the Universe at z, 6MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003Elizabeth R. Stanway ABSTRACT We determine the space density of UV-luminous starburst galaxies at z, 6 using deep HST ACS SDSS- i, (F775W) and SDSS- z, (F850LP) and VLT ISAAC J and Ks band imaging of the Chandra Deep Field South. We find eight galaxies and one star with (i,,z,) > 1.5 to a depth of z,AB= 25.6 (an 8, detection in each of the 3 available ACS epochs). This corresponds to an unobscured star formation rate of ,15 h,270 M, yr,1 at z= 5.9, equivalent to L* for the Lyman-break population at z= 3,4 (,,= 0.7, ,M= 0.3). We are sensitive to star-forming galaxies at 5.6 ,z, 7.0 with an effective comoving volume of ,1.8 × 105h,370 Mpc3 after accounting for incompleteness at the higher redshifts due to luminosity bias. This volume should encompass the primeval subgalactic-scale fragments of the progenitors of about a thousand L* galaxies at the current epoch. We determine a volume-averaged global star formation rate of (6.7 ± 2.7) × 10,4h70 M, yr,1 Mpc,3 at z, 6 from rest-frame UV selected starbursts at the bright end of the luminosity function: this is a lower limit because of dust obscuration and galaxies below our sensitivity limit. This measurement shows that at z, 6 the star formation density at the bright end is a factor of ,6 times less than that determined by Steidel et al. for a comparable sample of UV-selected galaxies at z= 3,4, and so extends our knowledge of the star formation history of the Universe to earlier times than previous work and into the epoch where reionization may have occurred. [source] Stellar contributors to the hard X-ray background?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2000Priyamvada Natarajan We use simple energetic arguments to estimate the contribution of massive X-ray binaries and supernova remnants to the cosmic X-ray background (XRB) at energies in excess of 2 keV. Recent surveys have shown that active galactic nuclei (AGN) probably account for most of the hard XRB (E>2 keV), but there have been many suggestions that star-forming galaxies could emerge at fainter fluxes and perhaps account for a significant fraction of the soft and hard X-ray energy density. Assuming that the formation rate of massive X-ray binaries (MXRBs) traces the global star-formation rate, we find that their integrated contribution to the hard XRB can be estimated and is shown to be small (at less than the 1 per cent level). Similarly, the integrated flux of supernovae (SN) is also shown to be insignificant, or at most comparable to MXRBs. AGN therefore remain the most viable candidates for producing the hard XRB, unless additional processes can be shown to dominate the global hard X-ray emission in distant starburst galaxies. [source] The FIRST radio survey: Panchromatic properties of FIRST radio sources identified in the Boötes and Cetus fieldsASTRONOMISCHE NACHRICHTEN, Issue 1 2009K. El Bouchefry Abstract In this paper the availability of multi-wavelength optical/infrared information of FIRST (Faint Images of the Radio Sky at 20 cm) radio sources counterparts over ,9.2 deg2 in the Boötes field and ,2.4 deg2 in the Cetus field is exploited to infer the physical properties of the faint radio population. The radio sources optically identified have been divided into resolved galaxies and stellar-like objects finding that the faint radio population is mainly composed of early-type galaxies with very red colour (Bw , R , 4.6). A total number of 57 counterparts of FIRST radio sources have extremely red colour (R , K , 5). Photometric redshift from Hyperz implies that the Extremely Red Objects (EROs) counterparts to FIRST radio sources are mostly located in the range z = 0.7,2, with the bulk of the population at z , 1. Taking advantage of the near infrared imaging with FLAMEX (FLAMINGOS Extragalactic Infrared Survey), the EROs counterparts to FIRST radio sources are separated into passively-evolving and dusty star-forming galaxies using their RJK colours; the relatively blue J , K of these galaxies suggest that most are old elliptical galaxies (18/25) rather than dusty starburst galaxies (7/25). A total of 15 Distant Red Galaxy (DRGs) have been identified as counterparts to FIRST radio sources in the Cetus field and 3 DRGs in the Boötes field with J , K > 2.3 (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A QSO host galaxy and its Ly, emission at z= 6.43,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009Tomotsugu Goto ABSTRACT Host galaxies of highest redshift quasi-stellar objects (QSOs) are of interest; they provide us with a valuable opportunity to investigate physics relevant to the starburst,active galactic nuclei (AGN) connection at the earliest epoch of the Universe, with the most luminous black holes. Here, we report an optical detection of an extended structure around a QSO at z= 6.43 in deep z,- and zr -band images of the Subaru/Suprime-Cam. Our target is CFHQS J2329-0301 (z= 6.43), the highest redshift QSO currently known. We have carefully subtracted a point spread function (PSF) constructed using nearby stars from the images. After the PSF (QSO) subtraction, a structure in the z, band extends more than 4 arcsec on the sky (Re= 11 kpc), and, thus, is well resolved (16, detection). The PSF-subtracted zr -band structure is in a similar shape to that in the z, band, but less significant with a 3, detection. In the z, band, a radial profile of the QSO+host shows a clear excess over that of the averaged PSF in 0.8,3 arcsec radius. Since the z, band includes a Ly, emission at z= 6.43, we suggest the z, flux is a mixture of the host (continuum light) and its Ly, emission, whereas the zr -band flux is from the host. Through a SED modelling, we estimate 40 per cent of the PSF-subtracted z,-band light is from the host (continuum) and 60 per cent is from Ly, emission. The absolute magnitude of the host is M1450=,23.9 (cf. M1450=,26.4 for the QSO). A lower limit of the SFR(Ly,) is 1.6 M, yr,1 with stellar mass ranging from 6.2 × 108 to 1.1 × 1010 M, when 100 Myr of age is assumed. The detection shows that a luminous QSO is already harboured by a large, star-forming galaxy in the early Universe only after ,840 Myr after the big bang. The host may be a forming giant galaxy, co-evolving with a super-massive black hole. [source] A case of mistaken identity?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007GRB 060912A, short GRB divide, the nature of the long ABSTRACT We investigate the origin of the GRB 060912A, which has observational properties that make its classification as either a long or short burst ambiguous. Short-duration gamma-ray bursts (SGRBs) are thought to have typically lower energies than long-duration bursts, can be found in galaxies with populations of all ages and are likely to originate from different progenitors to the long-duration bursts. However, it has become clear that duration alone is insufficient to make a distinction between the two populations in many cases, leading to a desire to find additional discriminators of burst type. GRB 060912A had a duration of 6 s and occurred only ,10 arcsec from a bright, low-redshift (z= 0.0936) elliptical galaxy, suggesting that this may have been the host, which would favour it being a short burst. However, our deep optical imaging and spectroscopy of the location of GRB 060912A using the Very Large Telescope (VLT) shows that GRB 060912A more likely originates in a distant star-forming galaxy at z= 0.937, and is most likely a long burst. This demonstrates the risk in identifying bright, nearby galaxies as the hosts of given gamma-ray bursts (GRBs) without further supporting evidence. Further, it implies that, in the absence of secure identifications, ,host' type, or more broadly discriminators that rely on galaxy redshifts, may not be good indicators of the true nature of any given GRB. [source] A star-forming galaxy at z= 5.78 in the Chandra Deep Field SouthMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003Andrew J. Bunker ABSTRACT We report the discovery of a luminous z= 5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an ,i -drop' from the GOODS public survey imaging with the Hubble Space Telescope/Advanced Camera for Surveys (object 3 in the work of Stanway, Bunker & McMahon 2003). The large colour of (i,,z,)AB= 1.6 indicated a spectral break consistent with the Lyman , forest absorption shortward of Lyman , at z, 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08 arcsec, so rhl < 0.5 h,170 kpc). We have obtained a deep (5.5 h) spectrum of this z,AB= 24.7 galaxy with the DEIMOS optical spectrograph on the Keck Telescope, and here we report the discovery of a single emission line centred on 8245 Å detected at 20, with a flux of f, 2 × 10,17 erg cm,2 s,1. The line is clearly resolved with detectable structure at our resolution of better than 55 km s,1, and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman , emission from a z= 5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using HST data. The velocity width (,vFWHM= 260 km s,1) and rest-frame equivalent width (WLy,rest= 20 Å) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization N v,1240- Å emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34 h,270 M, yr,1 (,M= 0.3, ,,= 0.7). This is the most luminous starburst known at z > 5. Our spectroscopic redshift for this object confirms the validity of the i,-drop technique of Stanway et al. to select star-forming galaxies atz, 6. [source] | ||||||||||