Range Of Star Formation Rates Research Articles

Galaxies atz≈ 4 and the Formation of Population II

We report the discovery of four high-redshift objects (3.3 < z < 4) observed behind the rich cluster CL0939+4713 (Abell 851). One object (DG 433) has a redshift of z=3.3453; the other three objects have redshifts of z\approx 4: A0 at z=3.9819, DG 353 and P1/P2 at z=3.9822. It is possible that all four objects are being lensed in some way by the cluster, DG 433 being weakly sheared, A0 being strongly sheared, and DG 353 and P1/P2 being an image pair of a common source object; detailed modelling of the cluster potential will be necessary to confirm this hypothesis. The weakness of common stellar wind features like N V and especially C IV in the spectra of these objects argues for sub-solar metallicities, at least as low as the SMC. DG 353 and DG 433, which have ground-based colors, are moderately dusty [E_{int}(B-V) < 0.15], similar to other z>3 galaxies. Star formation rates range from 2.5 (7.8) h^{-2} to 22. (78.) h^{-2} M_{\odot}/yr, for q_0=0.5 (0.05), depending on assumptions about gravitational lensing and extinction, also typical of other z>3 galaxies. These objects are tenatively identified as the low-metallicity proto-spheroid clumps that will merge to form the Population II components of today's spheroids.

Ultraviolet Imaging of NGC 3310: A Merger-driven Global Starburst

We present the first far-ultraviolet (FUV; λ ~ 1500 A) image of the nearby peculiar SAB(r)bc galaxy NGC 3310. The small 15'' (945 pc) diameter circumnuclear starburst ring is the most luminous structure, producing 30% of the total observed FUV luminosity. Diffuse emission from the inner disk (20'' < R < 40'') contributes another ~20% of the observed FUV flux. A linear feature (the arrow) appears to be a star-forming tidal feature. A diffuse arc observed at optical wavelengths (the bow) is not visible in the FUV and is probably a tidally induced shell composed of older stars. Mean star formation rates range from 0.031 M☉ yr-1 kpc-2 in the arrow to 2.1 M☉ yr-1 kpc-2 at the brightest FUV source. The striking similarity between the R1/4 law behavior of the FUV and B-band surface brightness profiles, combined with the very blue colors of NGC 3310, strongly argues that the present morphology is the result of a global starburst triggered by a merger with a dwarf companion.

Ionized Gas in the Halos of Edge-on Starburst Galaxies: Evidence for Supernova-driven Superwinds

view Abstract Citations (283) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ionized Gas in the Halos of Edge-on Starburst Galaxies: Evidence for Supernova-driven Superwinds Lehnert, Matthew D. ; Heckman, Timothy M. Abstract Supernova-driven galactic winds ("superwinds") have been invoked to explain many aspects of galaxy formation and evolution. Such winds should arise when the supernova rate is high enough to create a cavity of very hot shock-heated gas within a galaxy. This gas can then expand outward as a high-speed wind that can accelerate and heat ambient interstellar or circum-galactic gas causing it to emit optical line radiation and/or thermal X-rays. Theory suggests that such winds should be common in starburst galaxies and that the nature of the winds should depend on the star formation rate and distribution. In order to systematize our observational understanding of superwinds (determine their incidence rate and the dependence of their properties on the star formation that drives them) and to make quantitative comparisons with the theory of superwinds, we have analyzed data from an optical spectroscopic and narrow-band imaging survey of an infrared flux-limited (S_60 microns_ >= 5.4 Jy) sample of about 50 IR-warm (S_60 microns_/S_100 microns_ > 0.4), starburst galaxies whose stellar disks are viewed nearly edge-on (b/a ~> 2). This sample contains galaxies with infrared luminosities from ~10^10^-10^12^ L_sun_ and allows us to determine the properties of superwinds over a wide range of star formation rates. We have found that extraplanar emission-line gas is a very common feature of these edge-on, IR-bright galaxies and the properties of the extended emission-line gas are qualitatively and quantitatively consistent with the superwind theory. We can summarize these properties as morphological, ionization, dynamical, and physical. 1. Morphological properties.-Extraplanar filamentary and shell-like emission-line morphologies on scales of hundreds of parsecs to 10 kpc are common, there is a general "excess" of line emission along the minor axis, the minor axis emission-line "excess" correlates with "IR activity," and the minor axis emission-line "excess" also correlates with the relative compactness of the Hα emission. 2. Ionization properties.-Line ratios become more "shocklike" (high ratios of [N II] λ6583/Hα, [S II] λλ6716, 6731/Hα, and [O I] λ6300/Hα) at more extreme IR properties, the most "shocklike" line ratios occur far out along the minor axis, "shocklike" line ratios corresponds to broad emission lines, and the most extreme line ratios correspond to the most extreme IR properties, especially for the emission-line gas farthest out along the minor axis. 3. Dynamical properties.-Lines are broader along the minor axis than along the major axis, line widths correlate with the "IR activity," line widths correlate with line ratios, line widths do not correlate with rotation speed, minor axis shear (a measure of the systematic velocity change along the minor axis) correlates with "IR activity," minor axis shear correlates with axial ratio and implies that a face-on galaxy would have an outflow/inflow speed of 170_-80_^+150^ km s^-1^, and the starbursts show statistically blueward line profile asymmetries. 4. Physical properties.-Pressures in the nuclei of these galaxies are 3 orders of magnitude higher than the ambient pressure in the interstellar medium of our galaxy, and the pressure falls systematically with radius. While none of these results are in themselves proof of the superwind model, we believe that when the results are taken as a whole, the superwind hypothesis is very successful in explaining what we have observed. In addition, these results have implications for galaxy evolution and the nature of the intergalactic medium. Those galaxies with the best evidence for driving superwinds are those with large IR luminosities (L_IR_ ~> 10^44^ ergs s^-1^), large IR excesses (L_IR_/L_OPT_ ~> 2), and warm far-IR colors (S_60 microns_/S_100 microns_ ~> 0.5). Integrating over the local far-IR luminosity function for galaxies meeting the above criteria, multiplying by the age of the universe, and then dividing by the local space density of galaxies implies that superwinds have carried out ~5 x 10^8^ M_sun_ in metals and 10^59^ ergs in kinetic plus thermal energy per average (Schecter L^*^) galaxy over the history of the universe. We note that these two quantities are approximately equal to the mass of metals contained inside an average galaxy and the gravitational binding energy of an average galaxy, respectively. Even with the conservative assumptions of this calculation (we have neglected that star formation rates were presumably higher in the early universe), it is obvious that superwinds may have a major impact on the evolution of individual galaxies and the intergalactic medium by injecting mass, metals, and kinetic energy into the galactic halo and potentially the intergalactic medium. Publication: The Astrophysical Journal Pub Date: May 1996 DOI: 10.1086/177180 Bibcode: 1996ApJ...462..651L Keywords: GALAXIES: HALOS; GALAXIES: STARBURST; GALAXIES: ISM; INFRARED: GALAXIES; SHOCK WAVES; STARS: SUPERNOVAE: GENERAL full text sources ADS | data products SIMBAD (47) NED (46)

H II Regions in Four Galaxies in and near the Local Group

view Abstract Citations (65) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS H II Regions in Four Galaxies in and near the Local Group Hodge, Paul ; Miller, Bryan W. Abstract We present identifications, fluxes, and sizes for H II regions in three galaxies that are in or near the Local Group: WLM, UGC A86, and EGB 0427+63. A deep search for H II regions in a fourth galaxy, LGS 3, produced a negative result. Our results for UGC A86 indicate that, contrary to a previous suggestion, it is a single galaxy. Its disjointed appearance in broadband images apparently is caused by the presence of several star-forming regions of different ages. Our data, together with other information about it, especially its radial velocity, also suggest that this object is beyond the limits of the Local Group. The H II regions of the three galaxies in which they were detected show normal luminosity functions that fit power laws and normal size distributions that are reasonably well fitted by an exponential function. The calculated star formation rates range from zero for LGS 3 to 0.014 Msun yr-1 for UGC A86. Emission-line spectra of seven H II regions in the three galaxies allow abundances to be determined. We find that all are low in heavy elements, with mean values for O/H of approximately 7% solar. Publication: The Astrophysical Journal Pub Date: September 1995 DOI: 10.1086/176209 Bibcode: 1995ApJ...451..176H Keywords: GALAXIES: LOCAL GROUP; GALAXIES: STELLAR CONTENT; GALAXIES: STRUCTURE; ISM: ABUNDANCES; ISM: H II REGIONS; STARS: FORMATION full text sources ADS | data products SIMBAD (168) NED (165)

H-alpha imaging of galaxies in the Bootes void

We report H-alpha and continuum imaging of 12 galaxies in the Bootes void. The H-alpha emission in ten galaxies is due to star formation; one galaxy is probably a narrow emission line Active Galactic Nuclei (AGN), and one a Seyfert 1. Star formation rates range from 3-55 solar mass/yr, with the most active galaxies producing stars at almost three times the rate found in normal field disk systems. Eleven galaxies have strong H-alpha emission in the nucleus. The morphology of several of the galaxies is disturbed. There are at least five spirals, three of which are probably one-armed spirals, and three edge-on disk systems. Three galaxies not identifiable as spirals have H-alpha emission from regions outside the nuclear point source. 1510+4727, which has the highest rate of star formation in our sample, does not have the strong far-infrared emission expected from a galaxy experiencing significant star formation. The galaxies are quite luminous M(sub B) = -21 to -23 mag), and are not the type predicted to be found in voids.

Star Formation in Normal Irregular Galaxies

Normal, non-interacting irregular galaxies can be quite successful at forming stars. Therefore, spiral density waves are not necessary to a vigorous production of stars. Nevertheless, there is a large range in star-formation rates among irregular galaxies. Irregulars with common characteristics can have different overall levels of star-formation activity, so that the level of activity does not seem to be simple related to observable global properties of galaxian systems. The constant star formation rates of most normal irregulars also imply the existence of regulatory processes.