Significant Star Formation Activity Research Articles

GRB 191019A: A Short Gamma-Ray Burst in Disguise from the Disk of an Active Galactic Nucleus

Long and short gamma-ray bursts (GRBs), canonically separated at around 2 s duration, are associated with different progenitors: the collapse of a massive star and the merger of two compact objects, respectively. GRB 191019A was a long GRB (T 90 ∼ 64 s). Despite the relatively small redshift z = 0.248 and Hubble Space Telescope follow-up observations, an accompanying supernova was not detected. In addition, the host galaxy did not have significant star formation activity. Here we propose that GRB 191019A was produced by a binary compact merger, whose prompt emission was stretched in time by the interaction with a dense external medium. This would be expected if the burst progenitor was located in the disk of an active galactic nucleus, as supported by the burst localization close to the center of its host galaxy. We show that the light curve of GRB 191019A can be well modeled by a burst of intrinsic duration t eng = 1.1 s and of energy E iso = 1051 erg seen moderately off axis, exploding in a medium of density ∼107–108 cm−3. The double-peaked light curve carries the telltale features predicted for GRBs in high-density media, where the first peak is produced by the photosphere and the second by the overlap of reverse shocks that take place before the internal shocks could happen. This would make GRB 191019A the first confirmed stellar explosion from within an accretion disk, with important implications for the formation and evolution of stars in accretion flows and for gravitational-waves source populations.

Star-forming brightest cluster galaxies at z ∼ 0.4 in KiDS

Brightest cluster galaxies (BCGs) at the centers of clusters are among the most massive galaxies in the Universe. Their star formation history and stellar mass assembly are highly debated. Recent studies suggest the presence of an emerging population of intermediate-z star-forming and gas-rich BCGs, whose molecular gas reservoirs that feed star formation might be impacted by strong environmental processing. We have selected three of the most strongly star-forming z ∼ 0.4 BCGs in the equatorial field of the Kilo-Degree Survey (KiDS) and observed them with the IRAM 30 m telescope in the first three CO transitions. We found clear double-horn CO(1→0) and CO(3→2) emission for the KiDS 1433 BCG, yielding a large molecular gas reservoir with MH2 = (5.9 ± 1.2)×1010 M⊙ and a high gas-to-stellar mass ratio MH2/M⋆ = (0.32−0.10+0.12). We thus increase the still limited sample of distant BCGs with detections in multiple CO transitions. The double-horn emission for the KiDS 1433 BCG implies a low gas concentration, while a modeling of the spectra yields an extended molecular gas reservoir, with a characteristic radius of ∼(5−7) kpc, which is reminiscent of the mature extended-disk phase that is observed in some local BCGs. For the remaining two BCGs, we are able to set robust upper limits of MH2/M⋆ < 0.07 and < 0.23, which are among the lowest for distant BCGs. We then combined our observations with available stellar, star formation, and dust properties of the targeted BCGs, and compared them with a sample of ∼100 distant cluster galaxies, including additional intermediate-z BCGs, with observations in CO from the literature. Altogether, our analysis shows that the molecular gas properties of star-forming BCGs are heterogeneous. On the one hand, gas-rich BCGs show extended gas reservoirs that sustain the significant star formation activity, but the efficiency is low, which is reminiscent of recent gas infall. On the other hand, the existence of similarly star forming but gas-poor BCGs suggests that gas depletion precedes star formation quenching.

Dynamics of Molecular Gas in the Central Region of the Quasar I Zwicky 1

We present a study of the molecular gas distribution and kinematics in the cicumnuclear region (radii ≲2 kpc) of the z ≈ 0.061 quasar I Zwicky 1 using a collection of available Atacama Large Millimeter/submillimeter Array observations of the carbon monoxide (CO) emission. With an angular resolution of ∼0.″36 (corresponding to ∼400 pc), the host-galaxy substructures including the nuclear molecular gas disk, spiral arms, and a compact bar-like component are resolved. We analyzed the gas kinematics based on the CO image cube and obtained the rotation curve and radial distribution of velocity dispersion. The velocity dispersion is about 30 km s−1 in the outer CO disk region and rises up to ≳100 km s−1 at radius ≲1 kpc, suggesting that the central region of the disk is dynamically hot. We constrain the CO-to-H2 conversion factor, α CO, by modeling the cold gas disk dynamics. We find that, with prior knowledge about the stellar and dark matter components, the α CO value in the circumnuclear region of this quasar host galaxy is , which is between the value reported in ultraluminous infrared galaxies and in the Milky Way. The central 1 kpc region of this quasar host galaxy has significant star formation activity, which can be identified as a nuclear starburst. We further investigate the high-velocity dispersion in the central region. We find that the interstellar medium (ISM) turbulent pressure derived from the gas velocity dispersion is in equilibrium with the weight of the ISM. This argues against extra power from active galactic nuclei feedback that significantly affects the kinematics of the cold molecular gas.

The nearby extreme accretion and feedback system PDS 456: finding a complex radio-emitting nucleus

ABSTRACT When a black hole accretes close to the Eddington limit, the astrophysical jet is often accompanied by radiatively driven, wide-aperture and mildly relativistic winds. Powerful winds can produce significant non-thermal radio emission via shocks. Among the nearby critical accretion quasars, PDS 456 has a very massive black hole (about 1 billion solar masses), shows a significant star-forming activity (about 70 solar masses per year), and hosts exceptionally energetic X-ray winds (power up to 20 per cent of the Eddington luminosity). To probe the radio activity in this extreme accretion and feedback system, we performed very long baseline interferometric (VLBI) observations of PDS 456 at 1.66 GHz with the European VLBI Network and the enhanced Multi-Element Remotely Linked Interferometry Network. We find a rarely seen complex radio-emitting nucleus consisting of a collimated jet and an extended non-thermal radio emission region. The diffuse emission region has a size of about 360 pc and a radio luminosity about three times higher than that of the nearby extreme starburst galaxy Arp 220. The powerful nuclear radio activity could result either from a relic jet with a peculiar geometry (nearly along the line of sight) or more likely from diffuse shocks formed naturally by the existing high-speed winds impacting on high-density star-forming regions.

UV and Lyα luminosity functions of galaxies and star formation rate density at the end of HI reionization from the VIMOS UltraDeep Survey (VUDS)

Context. The star formation rate density (SFRD) evolution presents an area of great interest in the studies of galaxy evolution and reionization. The current constraints of SFRD at z > 5 are based on the rest-frame UV luminosity functions with the data from photometric surveys. The VIMOS UltraDeep Survey (VUDS) was designed to observe galaxies at redshifts up to ∼6 and opened a window for measuring SFRD at z > 5 from a spectroscopic sample with a well-controlled selection function. Aims. We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization (5.0 ≤ z ≤ 6.6) from a large sample of 49 galaxies with spectroscopically confirmed redshifts. We determine the rest-frame UV and Lyα luminosity functions and use them to calculate SFRD at the median redshift of our sample z = 5.6. Methods. We selected a sample of galaxies at 5.0 ≤ zspec ≤ 6.6 from the VUDS. We cleaned our sample from low redshift interlopers using ancillary photometric data. We identified galaxies with Lyα either in absorption or in emission, at variance with most spectroscopic samples in the literature where Lyα emitters (LAE) dominate. We determined luminosity functions using the 1/Vmax method. Results. The galaxies in this redshift range exhibit a large range in their properties. A fraction of our sample shows strong Lyα emission, while another fraction shows Lyα in absorption. UV-continuum slopes vary with luminosity, with a large dispersion. We find that star-forming galaxies at these redshifts are distributed along the main sequence in the stellar mass vs. SFR plane, described with a slope α = 0.85 ± 0.05. We report a flat evolution of the specific SFR compared to lower redshift measurements. We find that the UV luminosity function is best reproduced by a double power law, while a fit with a Schechter function is only marginally inferior. The Lyα luminosity function is best fitted with a Schechter function. We derive a logSFRDUV(M⊙ yr−1 Mpc−3) = −1.45+0.06−0.08 and logSFRDLyα(M⊙ yr−1 Mpc−3) = −1.40+0.07−0.08. The SFRD derived from the Lyα luminosity function is in excellent agreement with the UV-derived SFRD after correcting for IGM absorption. Conclusions. Our new SFRD measurements at a mean redshift of z = 5.6 are ∼0.2 dex above the mean SFRD reported in Madau & Dickinson (2014, ARA&A, 52, 415), but in excellent agreement with results from Bouwens et al. (2015a, ApJ, 803, 34). These measurements confirm the steep decline of the SFRD at z > 2. The bright end of the Lyα luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest LAE at these redshifts. LAE with equivalent width EW > 25 Å contribute to about 75% of the total UV-derived SFRD. While our analysis favors low dust content in 5.0 < z < 6.6, uncertainties on the dust extinction correction and associated degeneracy in spectral fitting will remain an issue, when estimating the total SFRD until future surveys extending spectroscopy to the NIR rest-frame spectral domain, such as with JWST.

An Extended Emission Line Region around Mrk 1172

AbstractWe serendipitously found an intriguing Extended Emission Line Region (EELR) near the quiescent and massive early-type Mrk 1172, with a projected extension of approximately 14 × 14 kpc. Its irregular shape, high gas content, strong emission lines and proximity to an isolated possible faded quasar raise questions about the ionization of this gas and the nature of this object. Analyzing the stellar population in both objects we observe that the EELR has a dominance of young-intermediate and intermediate stellar populations (200 Myr < t < 1 Gyr) with significant star formation activity, while Mrk 1172 is dominated by old stellar population (t > 5 Gyr). BPT diagnostic diagrams indicate that the gas in the EELR is photoionized by hot massive stars rather than by a hard radiation field or by shocks. Further analysis on abundances of the gas and its kinematics shall be performed to better comprehend the nature of this object and how it is interacting with Mrk 1172.

Star formation suppression and bar ages in nearby barred galaxies

We present new spectroscopic data for 21 barred spiral galaxies, which we use to explore the effect of bars on disk star formation, and to place constraints on the characteristic lifetimes of bar episodes. The analysis centres on regions of heavily suppressed star formation activity, which we term 'star formation deserts'. Long-slit optical spectroscopy is used to determine H beta absorption strengths in these desert regions, and comparisons with theoretical stellar population models are used to determine the time since the last significant star formation activity, and hence the ages of the bars. We find typical ages of approx. 1 Gyr, but with a broad range, much larger than would be expected from measurement errors alone, extending from about 0.25 Gyr to more than 4 Gyr. Low-level residual star formation, or mixing of stars from outside the 'desert' regions, could result in a doubling of these age estimates. The relatively young ages of the underlying populations coupled with the strong limits on the current star formation rule out a gradual exponential decline in activity, and hence support our assumption of an abrupt truncation event.

OMEGA – OSIRIS Mapping of Emission-line Galaxies in A901/2: II. – Environmental influence on integrated star formation properties and AGN activity

We present a study of the star formation and AGN activity for galaxies in the Abell 901/2 multi-cluster system at z~0.167 as part of the OMEGA survey. Using Tuneable Filter data obtained with the OSIRIS instrument at the GTC we produce spectra covering the Halpha and [N II] spectral lines for more than 400 galaxies. Using optical emission-line diagnostics, we identify a significant number of galaxies hosting AGN, which tend to have high masses and a broad range of morphologies. Moreover, within the environmental densities probed by our study, we find no environmental dependence on the fraction of galaxies hosting AGN. The analysis of the integrated Halpha emission shows that the specific star formation rates (SSFRs) of a majority of the cluster galaxies are below the field values for a given stellar mass. We interpret this result as evidence for a slow decrease in the star formation activity of star-forming galaxies as they fall into higher-density regions, contrary to some previous studies which suggested a rapid truncation of star formation. We find that most of the intermediate- and high-mass spiral galaxies go through a phase in which their star formation is suppressed but still retain significant star-formation activity. During this phase, these galaxies tend to retain their spiral morphology while their colours become redder. The presence of this type of galaxies in high density regions indicates that the physical mechanism responsible for suppressing star-formation affects mainly the gas component of the galaxies, suggesting that ram-pressure stripping or starvation are potentially responsible.

The Evolved Stellar Content of NGC 147, NGC 185, and NGC 205*

Broadband near-infrared images are used to probe the photometric properties of the brightest asymptotic giant branch (AGB) stars within 2' of the centers of the dwarf elliptical galaxies NGC 147, NGC 185, and NGC 205. Sequences originating from oxygen-rich M giants and C stars are clearly distinguished on the (K, H - K) and (K, J - K) color-magnitude diagrams. Based on the peak brightness and color of the M giant sequences, ages of 1 and 0.1 Gyr are predicted for the most recent significant star-forming events in NGC 185 and NGC 205, respectively. The bolometric luminosity function of M giants in NGC 205 is flatter than in NGC 185, in agreement with studies at wavelengths shortward of 1 μm. The most luminous AGB stars in NGC 147 are well mixed with fainter stars throughout the area surveyed in this galaxy, and the peak brightness of the M giant sequence indicates that the most recent significant star-forming activity occurred ~3 Gyr in the past. The C star contents of the three galaxies are compared in two ways. First, the notion of a specific frequency measurement for C stars, in which C star counts per unit magnitude are normalized to a common integrated K-band brightness using published surface photometry, is introduced. The specific frequencies of C stars outside the areas of most recent star formation agree in all three galaxies. Second, comparisons are made using the integrated brightness from C stars, which is normalized to the integrated light from M giants and the integrated light from all stars. The fractional contribution made by C stars to the total AGB light in the K-band is found to be highest in NGC 147 and lowest in the central regions of NGC 205, which is qualitatively consistent with model predictions. The fractional contribution that C stars make to the total K-band light is found to be constant both within and between galaxies, with C stars contributing 2% of the total K-band light. We conclude that, when averaged over timescales of a few gigayears, these galaxies have turned similar fractions of gas and dust, normalized according to total galaxy mass, into stars. We argue that the material for star formation likely originated in well-regulated reservoirs and demonstrate that the mass of gas needed to fuel star formation during intermediate epochs could have been supplied by winds from evolved stars. Finally, multiepoch data are used to investigate the incidence of long-period variables (LPVs) in NGC 185 and NGC 205. While tight constraints cannot be placed on the LPV content of NGC 205, roughly 70% of the stars with MK between -7.5 and -8.0 in the central regions of NGC 185 appear to be LPVs with amplitudes similar to those of LPVs in the LMC.

The Millennium Galaxy Catalogue: on the natural subdivision of galaxies

The distribution of global photometric, spectroscopic, structural and morphological parame- ters for a well-defined sample of 350 nearby galaxies has been examined. The usual trends were recovered demonstrating that E/S0 galaxies are redder, more quiescent, more centrally concentrated and possess larger Sersic indices than late-type galaxies. Multivariate statistical analyses were performed to examine the distribution of all parameters simultaneously. The main result of these analyses was the existence of only two classes of galaxies, corresponding closely to early and late types. Linear discriminant analysis (LDA) was able to reproduce the classifications of early- and late-type galaxies with high success, but further refinement of galaxy types was not reproduced in the distribution of observed galaxy properties. A principal components analysis (PCA) showed that the major variance of the parameter set corresponded to a distinction between early and late types, highlighting the importance of the distinction. A hierarchical clustering analysis (HCA) revealed only two clear natural classes within the parameter set, closely corresponding to early and late types. Early and late types are clearly distinct and the distinction is of fundamental importance. In contrast, late types from Sa to Irr are smoothly distributed throughout the parameter space. A population of galaxies classified by eye as elliptical/lenticular, and exhibiting concentration indices similar to early types were found to have a significant star formation activity. These galaxies are preferentially faint, suggesting they are low-mass systems. Ke yw ords: galaxies: evolution - galaxies: fundamental parameters.

First sources in infrared light: stars, supernovae and miniquasars

The cosmic infrared background (IRB) at wavelengths between 1 and 3 μm provides a useful probe of early star formation prior to and during reionization. To explain the high optical depth to electron scattering, as measured by the Wilkinson Microwave Anisotropy Probe (WMAP), one requires significant star formation activity at redshifts of 10 and higher. In addition to massive stars, the IRB flux may be contributed by a population of early miniquasars. We study the relative contributions from first stars, supernovae and quasars to the IRB for reasonable star formation rates at high redshift. If miniquasars radiate efficiently at the Eddington limit, current background measurements limit the fraction of mass in first stars that is converted to seed black holes to be roughly less than 10 per cent. In the case of supernovae, though an individual supernova is much brighter than the progenitor star, due to the shorter lifetime (of the order of a few months), the fractional contribution to the IRB remains at a level of 10 per cent and below when compared to the same contribution from stars. The bright supernovae may, however, be directly detectable by future large ground-based and space telescopes.

The Cosmological Evolution of Metal Enrichment in Quasar Host Galaxies

We study the gas metallicity of quasar hosts using cosmological hydrodynamic simulations of the ?CDM model. Galaxy formation in the simulations is coupled with a prescription for black hole activity, enabling us to study the evolution of the metal enrichment in quasar hosts and hence explore the relationship between star/spheroid formation and black hole growth/activity. In order to assess effects of numerical resolution, we compare simulations with different particle numbers and box sizes. We find a steep radial metallicity gradient in quasar host galaxies, with gas metallicities close to solar values in the outer parts but becoming supersolar in the center. The hosts of the rare bright quasars at z ~ 5-6 have star formation rates of several hundred M? yr-1 and halo masses of order ~1012 M?. Already at these redshifts they have supersolar (Z/Z? ~ 2-3) central metallicities, with a mild dependence of metallicity on luminosity, consistent with observed trends. The mean value of metallicity is sensitive to the assumed quasar lifetime, providing a useful new probe of this parameter. We find that lifetimes from 107 to 4 ? 107 yr are favored by comparison with observational data. In both the models and observations, the rate of evolution of the mean quasar metallicity as a function of redshift is generally flat out to z ~ 4-5. Beyond the observed redshift range and out to redshift z = 6-8, we predict a slow decline of the mean central metallicity toward solar and slightly subsolar values (Z/Z? ~ 0.4-1) as we approach the epoch of the first significant star formation activity.

The Star Formation History and Morphological Evolution of the Draco Dwarf Spheroidal Galaxy

The photometric and morphological properties, as well as the star formation history, of the Draco dwarf spheroidal galaxy are analyzed on the basis of wide-field CCD photometry of the resolved stars covering about 1 deg2. Draco is at a distance of d = 80 ? 7 kpc and has a metallicity, [Fe/H], of -1.8 ? 0.2. No metallicity gradient is detected. The star surface density distribution can be fitted by a single exponential law of scale length ? = 50 ? 01. The central surface magnitude is ? = 24.4 ? 0.5, and the core radius is rc = 75 ? 03 (equivalent to rc = 175 ? 7 pc). Within errors, the same scale lengths are found for the density profiles along the semimajor and semiminor axes (rescaled to semimajor-axis units, using the ellipticity of the galaxy) of Draco. There are hence no evidences of a tidal tail associated with Draco. The tidal radius of the galaxy is found to be rt 42' (1 kpc). The possibility that the large mass-to-light relation in Draco could be accounted for by a convenient spatial orientation is tested. An upper limit to Draco's size along the line of sight is ~14 kpc. This is too small to account for the velocity dispersion of Draco if it were due to projection effects only, and it implies that other mechanisms (e.g., dark matter) are required. The stellar population of Draco is mainly old. Although some intermediate-age population is present in Draco, most of the star formation (up to 90%) took place before ~10 Gyr ago. No significant star formation activity is detected in the last ~2 Gyr. Two methods (partial model and subgiant) have been used to investigate the star formation history of Draco, both producing results in good qualitative agreement. No difference is found between the scale lengths of the distributions of old (9 Gyr) and young (~2?3 Gyr) stars, indicating either that both populations were formed under the same kinematic conditions, or that any initial difference was afterward erased.

Optical and CO Radio Observations of Poor Cluster Zwicky 1615.8+3505

The cluster Zwicky 1615.8+3505 is considered to be a dynamically young poor cluster. To investigate the morphology and star-formation activity of galaxies under the environment of a dynamically young poor cluster, we have performed V, R, and I surface photometry, optical low-resolution spectroscopy, and 12CO (J=1–0) line observations for member galaxies. Our data show that more than 90% of the observed galaxies show regular morphologies and no star-formation activities, indicating that the environment does not affect these galaxy properties. Among sixteen galaxies observed, only NGC 6104 shows a significant star-formation activity, and shows a distorted morphology, indicating a tidal interaction. This galaxy contains double knots, and only one knot possesses Seyfert activity, though the sizes and luminosities are similar to each other; we also discuss this feature.

Smoothed Particle Hydrodynamics Simulations of Counterrotating Disk Formation in Spiral Galaxies

We present the results of smoothed particle hydrodynamics (SPH) simulations of the formation of a massive counterrotating disk in a spiral galaxy. The current study revisits and extends (with SPH) previous work carried out with sticky particle gas dynamics, in which adiabatic gas infall and a retrograde gas-rich dwarf merger were tested as the two most likely processes for producing such a counterrotating disk. We report on experiments with a cold primary similar to our Galaxy, as well as a hot, compact primary modeled after NGC 4138. We have also conducted numerical experiments with varying amounts of prograde gas in the primary disk and an alternative infall model (a spherical shell with retrograde angular momentum). The structure of the resulting counterrotating disks is dramatically different with SPH. The disks we produce are considerably thinner than the primary disks and those produced with sticky particles. The timescales for counterrotating disk formation are shorter with SPH, because the gas loses kinetic energy and angular momentum more rapidly. Spiral structure is evident in most of the disks, but an exponential radial profile is not a natural by-product of these processes. The infalling gas shells that we tested produce counterrotating bulges and rings rather than disks. The presence of a considerable amount of preexisting prograde gas in the primary causes, at least in the absence of star formation, a rapid inflow of gas to the center and a subsequent hole in the counterrotating disk. For a normal counterrotating disk to form, there must be either little or no preexisting prograde gas in the primary, or its dissipative influence must be offset by significant star formation activity. The latter scenario, along with the associated feedback to the interstellar medium, may be necessary to produce a counterrotating disk similar in scale length and scale height to the primary disk. In general, our SPH experiments yield stronger evidence to suggest that the accretion of massive counterrotating disks drives the evolution of the host galaxies toward earlier (S0/Sa) Hubble types.

The Distribution of Mid- and Far-Infrared Emission in 10 Interacting Galaxy Systems

A sample of 10 interacting and merging galaxy systems has been mapped at mid-infrared (10 μm) and far-infrared (100–160 μm) wavelengths with spatial resolutions of 4''and 45'', respectively. The interacting and merging systems are known to be strong IRAS sources; however, the IRAS data contain limited information concerning the distribution of infrared emission between the two galaxies in each pair and no information on the distribution within each galaxy. The observations presented here show that in five of the seven paired systems, one galaxy is the dominant or the only infrared source. There is a good correlation between the Hα and infrared emission levels for these galaxies, indicating that the infrared emission is closely tied to dust heated by young stars. There is also a good spatial correlation between the Hα, infrared, and radio continuum morphologies of these systems, which further strengthens the belief that the infrared, as well as the radio emission, is associated with regions of active star formation. The 10 μm emission is concentrated around the nuclei of most of these galaxies, indicating that the highest levels of current star formation activity are also confined to the near-nuclear regions. Some systems, however, show evidence for significant star formation activity throughout the outer disk regions of the galaxies. All the sample galaxies that are bright in the infrared also have optical indications of high levels of star formation or nuclear activity, suggesting that these conditions are necessary in order for a galaxy to exhibit excess infrared emission.

Far-infrared properties of early-type galaxies

view Abstract Citations (26) References (38) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-Infrared Properties of Early-Type Galaxies Mazzei, P. ; de Zotti, G. Abstract We have investigated the IRAS colors and the far-IR to optical luminosity ratios of a complete sample of elliptical and S0 galaxies brighter than B_T_ = 12. On the average, elliptical galaxies emit in the far-IR less than 1% of their bolometric luminosity; S0 galaxies are about a factor of 3 brighter in the far-IR. There is a considerable spread in the far-IR properties of individual galaxies. On the average, the photospheric emission of red giant stars can account for 50%-60% of the 12 micron flux from early-type galaxies; the contribution from diffuse dust at this wavelength is <10% in the case of elliptical galaxies and may amount to 20%-40% for S0 galaxies. An additional, ~30%-40%, contribution from circumstellar emission from evolved giants with mass loss (particularly OH/IR stars) seems to be required in the case of elliptical galaxies. This suggests a small but significant star-formation activity in these galaxies at a look-back time of 1-2 Gyr, corresponding to about 10% of that typical of a disk galaxy having the same V-band luminosity. As for S0 galaxies, the larger diffuse dust emission may swamp to some extent that of circumstellar dust, which is indicated to comprise, on the average, <~20% of the far-IR emission. The weak emission from diffuse interstellar dust, detected mostly at 60 microns and 100 microns, has color temperatures similar to those of disk galaxies; as in the case of the latter, a warm dust component is suggested, associated to star-forming regions, in addition to a cooler component, heated by the general interstellar radiation field. The implied star formation would be a few percent of that of disk galaxies of similar V-band luminosity and could account for a fraction of the observed UV branch of early-type galaxies. Publication: The Astrophysical Journal Pub Date: May 1994 DOI: 10.1086/174042 arXiv: arXiv:astro-ph/9402005 Bibcode: 1994ApJ...426...97M Keywords: Elliptical Galaxies; Far Infrared Radiation; Infrared Astronomy; Infrared Spectra; Interstellar Matter; Lenticular Bodies; Luminosity; Red Giant Stars; Spiral Galaxies; Astronomical Catalogs; Infrared Astronomy Satellite; Satellite-Borne Instruments; Star Formation Rate; Stellar Envelopes; Astrophysics; GALAXIES: ELLIPTICAL AND LENTICULAR; CD; GALAXIES: ISM; GALAXIES: SPIRAL; GALAXIES: STELLAR CONTENT; INFRARED: GALAXIES; Astrophysics E-Print: tex, 9 pages, 6 figures upon request full text sources arXiv | ADS | data products SIMBAD (1)

Gasdynamics and star formation in interacting and merging galaxies

view Abstract Citations (60) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gasdynamics and Star Formation in Interacting and Merging Galaxies Olson, Kevin M. ; Kwan, John Abstract In this paper we describe several additional simulations to those described in Olson and Kwan. We consider the effects various parameters have on the interaction of two galaxies and on the gas cloud collisions which are induced to occur. Increasing the angle of inclination between the spin axis of the galaxy which contains gas clouds and the orbital angular momentum vector, decreasing the mass of the perturbing galaxy, and increasing the kinetic energy of the interaction all have the effect of reducing the perturbation. A case where both galaxies contain gas clouds and the galaxies merge was also studied. As in Olson and Kwan, most of the cloud-cloud collisions which are induced by the interaction are disruptive and a large number of massive clouds is usually not produced. Based on these calculations and those described in Olson and Kwan, we suggest that if the burst of star formation triggered by the interaction of two galaxies occurs near closest approach, it may be related to the large number of disruptive cloud-cloud collisions which are induced. Monitoring the amount of gas mass involved in these collisions allows us to estimate the star-formation rate and the luminosity of the galaxy. We find that the parameters considered here can, to a large degree, account for the broad range of observed ratios of the far-infrared luminosity to molecular gas mass in interacting and merging galaxies. We also show that the radial location of the enhanced star formation depends on these parameters and that, while a large fraction of interacting galaxies which possess strong morphological peculiarities have elevated rates of star formation in or near their nuclei, a certain fraction also have elevated rates of star formation in their disks with no significant star-formation activity being induced in their nuclei. Publication: The Astrophysical Journal Pub Date: October 1990 DOI: 10.1086/169208 Bibcode: 1990ApJ...361..426O Keywords: Gas Dynamics; Interacting Galaxies; Interstellar Gas; Star Formation; Data Simulation; Molecular Clouds; Astrophysics; GALAXIES: INTERACTIONS; STARS: FORMATION full text sources ADS | data products SIMBAD (2)

Spectral synthesis in the ultraviolet. II - Stellar populations and star formation in blue compact galaxies

view Abstract Citations (192) References (86) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral Synthesis in the Ultraviolet. II. Stellar Populations and Star Formation in Blue Compact Galaxies Fanelli, Michael N. ; O'Connell, Robert W. ; Thuan, Trinh X. Abstract Far-UV spectra of seven blue compact galaxies have been obtained with the IUE satellite. These objects span a range in luminosity of -21 <= M_B_ <= -13. We have investigated their stellar content and star formation history by applying the technique of optimizing population synthesis utilizing the library of far-UV stellar spectra developed by Fanelli, O'Connell, and Thuan. The far-UV absorption-line spectra of these galaxies are clearly composite, with the signatures of main-sequence types between O3 and mid-A. Most of the low-ionization absorption lines have a stellar origin. The Si IV and C IV features in several objects have P Cygni profiles. In Haro 1 the strength of Si IV indicates a significant blue supergiant population. The metal-poor blue compact dwarf Mrk 209 displays weak absorption lines, evidence that the stellar component has the same low metallicity as observed in the ionized gas (Z ~ 0.1 Z_sun_). Good fits to the data are obtained with the synthesis technique. We find that the solutions yield stellar luminosity functions which display large discontinuities, indicative of discrete star formation episodes or bursts. Continuous star formation cannot account for the observations. The current burst of star formation appears to have lasted for less than 10 Myr. In all cases except Mrk 209 there is evidence of earlier star formation episodes. For Haro 2 there were at least two earlier bursts, the most recent of which ended not more than ~20 Myr ago. The A star populations in our models point to significant star formation activity 500 Myr or more ago. In the cases other than that of Haro 2, we cannot distinguish between a few isolated bursts and a continuing series of short bursts separated by ~20-30 Myr. The amount of UV extinction is found to be low, 0.0 <~ E(B- V) <~ 0.35, significantly smaller than values derived from the Balmer decrement for the same object. The UV light preferentially emerges through windows of low optical depth. We find evidence for a positive correlation between the amount of UV extinction and the metallicity of the galaxy. UV synthesis provides an independent estimate of the current ionizing star content which appears to be in agreement with estimates based on observations in the visible, radio, and infrared. Star formation rates can also be estimated for the hot stars detected directly in the UV, and these rates highlight the intensity of the starbursts. In the more luminous galaxies Haro 1 and Haro 15, ~3 M_sun_ yr^-1^ of gas is being converted into massive (m >~ 10 M_sun_) stars, a value independent of the nature of the initial mass function. Publication: The Astrophysical Journal Pub Date: November 1988 DOI: 10.1086/166869 Bibcode: 1988ApJ...334..665F Keywords: Compact Galaxies; Star Distribution; Star Formation; Stellar Spectra; Ultraviolet Spectra; Absorption Spectra; Dwarf Galaxies; Main Sequence Stars; Stellar Luminosity; Supergiant Stars; Astrophysics; GALAXIES: STELLAR CONTENT; STARS: FORMATION; ULTRAVIOLET: SPECTRA full text sources ADS | data products NED (8) SIMBAD (7) MAST (1) INES (1) Related Materials (3) Part 1: 1987ApJ...321..768F Part 3: 1990ApJ...364..272F Part 4: 1992ApJS...82..197F