Hbeta Luminosities Research Articles

Star-formation rate in compact star-forming galaxies

We use the data for the Hbeta emission-line, far-ultraviolet (FUV) and mid-infrared 22 micron continuum luminosities to estimate star formation rates <SFR> averaged over the galaxy lifetime for a sample of about 14000 bursting compact star-forming galaxies (CSFGs) selected from the Data Release 12 (DR12) of the Sloan Digital Sky Survey (SDSS). The average coefficient linking <SFR> and the star formation rate SFR_0 derived from the Hbeta luminosity at zero starburst age is found to be 0.04. We compare <SFR>s with some commonly used SFRs which are derived adopting a continuous star formation during a period of ~100 Myr, and find that the latter ones are 2-3 times higher. It is shown that the relations between SFRs derived using a geometric mean of two star-formation indicators in the UV and IR ranges and reduced to zero starburst age have considerably lower dispersion compared to those with single star-formation indicators. We suggest that our relations for <SFR> determination are more appropriate for CSFGs because they take into account a proper temporal evolution of their luminosities. On the other hand, we show that commonly used SFR relations can be applied for approximate estimation within a factor of ~2 of the <SFR> averaged over the lifetime of the bursting compact galaxy.

Searching for metal-deficient emission-line galaxy candidates: the final sample of the SDSS DR12 galaxies

We present a spectroscopic study of metal-deficient dwarf galaxy candidates, selected from the SDSS DR12. The oxygen abundances were derived using the direct method in galaxies with the electron temperature-sensitive emission line [OIII]4363A measured with an accuracy better than 30%. The oxygen abundances for the remaining galaxies with larger uncertainties of the [OIII]4363A line fluxes were calculated using a strong-line semi-empirical method by Izotov and Thuan. The resulting sample consists of 287 low-metallicity candidates with oxygen abundances below 12+logO/H=7.65 including 23 extremely metal-deficient (XMD) candidates with 12+log O/H<7.35. Ten out of sixteen XMDs known so far (or ~60%) have been discovered by our team using the direct method. Three XMDs were found in the present study. We study relations between global parameters of low-metallicity galaxies, including absolute optical magnitudes, Hbeta luminosities (or equivalently star formation rates), stellar masses, mid-infrared colours, and oxygen abundances. Low-metallicity and XMD galaxies strongly deviate to lower metallicities in L-Z, L(Hbeta)-Z and Mstar-Z diagrams than in relations obtained for large samples of low-redshift, star-forming galaxies with non-restricted metallicities. These less chemically evolved galaxies with stellar masses ~10^6-10^8Msun, Hbeta luminosities ~10^38-10^41 erg/s, SFR~0.01-1.0Msun/yr, and sSFR~50 Gyr^-1 have physical conditions which may be characteristic of high-redshift low-mass star-forming galaxies which are still awaiting discovery.

TheL−σrelation for HII galaxies in green

The correlation between emission-line luminosity (L) and profile width (sigma) for HII Galaxies provides a powerful method to measure the distances to galaxies over a wide range of redshifts. In this paper we use SDSS spectrophotometry to explore the systematics of the correlation using the [OIII]5007 lines instead of Halpha or Hbeta to measure luminosities and line widths. We also examine possible systematic effects involved in measuring the profile-widths and the luminosities through different apertures. We find that the green L-sigma relation defined using [OIII]5007 luminosities is significantly more sensitive than Hbeta to the effects of age and the physical conditions of the nebulae, which more than offsets the advantage of the higher strength of the [OIII]5007 lines. We then explore the possibility of mixing [OIII]5007 profile-widths with SDSS Hbeta luminosities using the Hubble constant H0 to quantify the possible systematic effects. We find the mixed L(Hbeta) sigma[OIII] relation to be at least as powerful as the canonical L-sigma relation as a distance estimator, and we show that the evolutionary corrections do not change the slope and the scatter of the correlation, and therefore, do not bias the L-sigma distance indicator at high redshifts. Locally, however, the luminosities of the Giant HII Regions that provide the zero-point calibrators are sensitive to evolutionary corrections and may bias the Hubble constant if their mean ages, as measured by the equivalent widths of Hbeta, are significantly different from the mean age of the HII Galaxies. Using a small sample of 16 ad-hoc zero point calibrators we obtain a value of H0 = 66.4\pm4.5 km s^-1 Mpc^-1 for the Hubble constant, which is fully consistent with the best modern determinations, and that is not biased by evolutionary corrections.

The efficiency of ionizing photon production and the radiation energy balance in compact star-forming galaxies

We derive apparent and absolute ultraviolet (UV) magnitudes, and luminosities in the infrared (IR) range of a large sample of low-redshift (0<z<1) compact star-forming galaxies (CSFGs) selected from the Data Release 12 of the Sloan Digital Sky Survey (SDSS). These data are used to constrain the extinction law in the UV for our galaxies and to compare the absorbed radiation in the UV range with the emission in the IR range. We find that the modelled far- and near-UV apparent magnitudes are in good agreement with the observed GALEX magnitudes. It is found that galaxies with low and high equivalent widths EW(Hbeta) of the Hbeta emission line require different reddening laws with steeper slopes for galaxies with higher EW(H$\beta$). This implies an important role of the hard ionising radiation in shaping the dust grain size distribution. The IR emission in the range of 8-1000 mum is determined using existing data obtained by various infrared space telescopes. We find that the radiation energy absorbed in the UV range is nearly equal to the energy emitted in the IR range leaving very little room for hidden star formation in our galaxies. Using extinction-corrected Hbeta luminosities and modelled SEDs in the UV range we derive efficiencies of ionising photon production \xi for the entire sample of CSFGs. It is found that $\xi$ in CSFGs with high EW(Hbeta) are among the highest known for low- and high-redshift galaxies. If galaxies with similar properties existed at redshifts z=5-10, they could be considered as promising candidates for the reionisation of the Universe.

Dust emission in star-forming dwarf galaxies: General properties and the nature of the submm excess

We studied the global characteristics of dust emission in a large sample of emission-line star-forming galaxies. The sample consists of two subsamples. One subsample (SDSS sample) includes ~4000 compact star-forming galaxies from the SDSS, which were also detected in all four bands at 3.4, 4.6, 12, and 22 mum of the WISE all-sky survey. The second subsample (Herschel sample) is a sample of 28 compact star-forming galaxies observed with Herschel in the FIR range. Data of the Herschel sample were supplemented by the photometric data from the Spitzer observations, GALEX, SDSS, WISE, 2MASS, NVSS, and FIRST surveys, as well as optical and Spitzer spectra and data in sub-mm and radio ranges. It is found that warm dust luminosities of galaxies from the SDSS sample and cold and warm dust luminosities of galaxies from the Herschel sample are strongly correlated with Hbeta luminosities, which implies that one of the main sources of dust heating in star-forming galaxies is ionising UV radiation of young stars. Using the relation between warm and cold dust masses for estimating the total dust mass in star-forming galaxies with an accuracy better than ~0.5 dex is proposed. On the other hand, it is shown for both samples that dust temperatures do not depend on the metallicities. The dust-to-neutral gas mass ratio strongly declines with decreasing metallicity, similar to that found in other studies of local emission-line galaxies, high-redshift GRB hosts, and DLAs. On the other hand, the dust-to-ionised gas mass ratio is about one hundred times as high implying that most of dust is located in the neutral gas. It is found that thermal free-free emission of ionised gas in compact star-forming galaxies might be responsible for the sub-mm emission excess. This effect is stronger in galaxies with lower metallicities and is also positively affected by an increased star-formation rate.

Popstar evolutionary synthesis models – III. Photometric properties of young star clusters and mixed populations

This is the third paper of a series reporting the results from the POPSTAR evolutionary synthesis models. The main goal of this work is to present and discuss the synthetic photometric properties of Single Stellar Populations (SSPs) resulting from our POPSTAR code. Colours in the Johnson and SDSS systems, halpha and hbeta luminosities and equivalent widths, and ionising region size, have been computed for a wide range of metallicity (Z = 0.0001 - 0.05) and age (0.1 Myr to 20 Gyr). We demonstrate the importance of the contribution of emission lines to broader-band photometry when characterising stellar populations, through the presentation of both contaminated and non-contaminated colours (in both the Johnson and SDSS systems). The tabulated colours include stellar and nebular components, in addition to line emission. The main application of these models is the determination of physical properties of a given young ionising cluster, when only photometric observations are available; for an isolated star forming region, the young star cluster models can be used, free from the contamination of any underlying background stellar population. In most cases, however, the ionising population is usually embedded in a large and complex system, and the observed photometric properties result from the combination of a young star-forming burst and the underlying older population of the host. Therefore, the second objective of this paper is to provide a grid of models useful in the interpretation of mixed regions where the separation of young and old populations is not sufficiently reliable. We describe the set of PopStar Spectral Energy Distributions, the derived colours and other photometric parameters, for mixed populations where an underlying host population is combined in different mass ratios with a recent ionising burst.

TESTING DISK-LOCKING IN NGC 2264

We test analytic predictions from different models of magnetospheric accretion, which invoke disk-locking, using stellar and accretion parameters derived from models of low resolution optical spectra of 36 T Tauri stars (TTSs) in NGC 2264 (age~3 Myrs). Little evidence is found for models that assume purely dipolar field geometries; however, strong support is found in the data for a modified version of the X-wind model (Shu et al. 1994) which allows for non-dipolar field geometries. The trapped flux concept in the X-wind model is key to making the analytic predictions which appear supported in the data. By extension, our analysis provides support for the outflows predicted by the X-wind as these also originate in the trapped flux region. In addition, we find no support in the data for accretion powered stellar winds from young stars. By comparing the analysis presented here of NGC 2264 with a similar analysis of stars in Taurus (age~1-2 Myr), we find evidence that the equilibrium interaction between the magnetic field and accretion disk in TTS systems evolves as the stars grow older, perhaps as the result of evolution of the stellar magnetic field geometry. We compare the accretion rates we derive with accretion rates based on U-band excess, finding good agreement. In addition, we use our accretion parameters to determine the relationship between accretion and H-beta luminosity, again finding good agreement with previously published results; however, we also find that care must be used when applying this relationship due to strong chromospheric emission in young stars which can lead to erroneous results in some cases.

Star-forming galaxies with hot dust emission in the Sloan Digital Sky Survey discovered by the Wide-field Infrared Survey Explorer (WISE)

We present the results of a search for Sloan Digital Sky Survey (SDSS) emission-line galaxies with very red 3.4mum - 4.6mum (W1-W2) colours in the Wide-field Infrared Survey Explorer (WISE) Preliminary Release Source Catalogue (PRSC) aiming to find objects with hot dust emission. For this purpose we considered a sample of ~16000 galaxies with strong emission lines selected out of a total of ~900000 SDSS spectra and identified them with the PRSC sources. We find that ~5000 sources out of the ~16000 SDSS galaxies are present in the PRSC, including ~1000 galaxies with sufficiently strong [OIII]4363 emission lines to permit reliable determinations of the oxygen abundance. No correlation of W1-W2 with metallicity is found. On the other hand, there is clear evidence for a redder W1-W2 index in galaxies with higher Hbeta luminosity and higher Hbeta equivalent width, implying that strong UV radiation from young starbursts efficiently heats interstellar dust to high temperatures. However, galaxies with very red colours W1-W2>2 mag, similar to that in the local extreme star-forming galaxy SBS 0335-052E, are very rare. In addition to three previously known sources, which are not present in our sample, we found only four such galaxies.

THE LICK AGN MONITORING PROJECT: ALTERNATE ROUTES TO A BROAD-LINE REGION RADIUS

It is now possible to estimate black hole masses across cosmic time, using broad emission lines in active galaxies. This technique informs our views of how galaxies and their central black holes coevolve. Unfortunately, there are many outstanding uncertainties associated with these "virial" mass estimates. One of these comes from using the accretion luminosity to infer a size for the broad-line region. Incorporating the new sample of low-luminosity active galaxies from our recent monitoring campaign at Lick Observatory, we recalibrate the radius-luminosity relation with tracers of the accretion luminosity other than the optical continuum. We find that the radius of the broad-line region scales as the square root of the X-ray and Hbeta luminosities, in agreement with recent optical studies. On the other hand, the scaling appears to be marginally steeper with narrow-line luminosities. This is consistent with a previously observed decrease in the ratio of narrow-line to X-ray luminosity with increasing total luminosity. The radius of the broad-line region correlates most tightly with Hbeta luminosity, while the X-ray and narrow-line relations both have comparable scatter of a factor of two. These correlations provide useful alternative virial BH masses in objects with no detectable optical/UV continuum emission, such as high-redshift galaxies with broad emission lines, radio-loud objects, or local active galaxies with galaxy-dominated continua.

THE STRUCTURE AND ENVIRONMENT OF H II GALAXIES

ABSTRACT H II galaxies are dwarf star forming galaxies found in objective prism surveys through their strong emission lines. They have been targets of extensive studies of their spectroscopic properties such as chemical abundances, physical conditions and kinematics. Little surface photometry work has been done on H II galaxies up to now. This thesis is primarily a CCD surface photometry study of the structural properties, optical colors and a statistical analysis of the environment of H II galaxies. In the chapter "The Morphology of H II Galaxies" I have used a sample of 39 H II galaxies with CCD images for a study of their overall morphology and luminosity profiles. The results show that H II galaxies can be classified in two main types: type I H II galaxies are luminous and have disturbed and irregular outer shapes while type II H II galaxies are less luminous and have regular shapes. The outer parts of profiles of all HIi galaxies are well represented by an exponential as in other types of known dwarf galaxies. In "The Dynamics of H II Galaxies" I have investigated the relation between the linear size of the starburst, luminosity and velocity dispersion. It is found that H II galaxies have similar relations as virialized systems which supports the gravitational origin of their overall kinematics. The possible bi-parametric behavior ("fundamental plane") of H II galaxies is also investigated. However, a conclusive answer to this question still requires more and better data. In "The Colors of H II Galaxies" I have presented a high spatial resolution CCD surface photometry study. The colors of the underlying stellar continuum within the starburst are obtained by removing the flux contribution of the emission lines in the broad band filters. Comparison with recent evolutionary population synthesis models show that the observational errors and the uncertainties in the models are still too large to put strict constraints on their past star formation history. However, the distribution of colors of the underlying galaxy in H II galaxies is similar to the colors of some dwarf galaxies which suggests a kinship of these with the quiescent phases of H II galaxies. In "The Environment of H II Galaxies" I have studied the environment of 51 H II galaxies for which I have CCD images, H-beta luminosity, velocity dispersion, H-beta equivalent width and oxygen abundance. The aim of the study is to check the tidal origin of the starburst in H II galaxies and the effect of the environment on their intrinsic properties. It is found that only 12 H II galaxies have a bright neighbour within a projected distance of 1 Mpc and 250 km s-1 in velocity difference. Surprisingly, isolated H II galaxies tend to be of high luminosity and disturbed morphology while H II galaxies with neighbours tend to be low luminosity regular H II galaxies. Furthermore, the metal abundance and the equivalent width of the emission lines in H II galaxies do not depend on the presence of a companion. These results are opposed to what is expected if interaction with a luminous companion is the main mechanism triggering the starbursts. It is also found a loose group of four H II galaxies with no luminous companion. For this, there is the additional difficulty of understanding how these starbursts are synchronized on time scales of less than 107 yrs in systems separated by ~1-2 Mpc.

A spectrophotometric study of BQS quasars

Flux-calibrated spectra of 39 low-redshift quasars from the Bright Quasar Survey (BQS) have been used to study a near-complete data set of optically selected quasars. Statistical partial rank analysis shows that the forbidden O III luminosity is more intimately connected to the H-beta luminosity, L(H-beta), than to observed continuum luminosity, L(cont). L(H-beta) is thus considered to be a better measure than L(cont) of the photoionizing luminosity. The effects of an orientation-dependent L(cont) on the rest-frame emission-line equivalent widths, EW(H-beta), and EW(forbidden O III), have been studied. It is found that scatter in the L(H-beta) - L(cont) relation is not due to a range in broad-line covering factor, and is inconsistent with one simple orientation scheme unless objects with very high disk inclination angles are excluded by the BQS selection criteria. It is demonstrated that there exists a correlation between the full width at half maximum of the H-beta line and L(H-beta), providing evidence for a gravitationally bound H-beta-emitting region and a scaling M(central) approximately proportional to L.

The evolutionary sequence of planetary nebulae

A first-order solution to the problem of nebular evolution is presented and used to construct photoionization models with the correct ionized gas geometry with respect to the central star. The models are used to investigate the evolution of the central star in terms of a transformed H-R diagram in which H-beta luminosity replaces stellar luminosity and the nebular excitation class takes the place of stellar effective temperature. It is shown that the optically thick PN in the Magellanic Clouds behave as ram-pressure confined H II regions trapped between the shocked remnants of AGB wind and the high-velocity stellar wind of the PN nuclei. 72 refs.

Two new blazar redshifts

Two-dimensional spectra for PKS 2208-137 obtained on July 27-28, 1984 at CFHT and for MC3 2032 + 107 obtained on June 13-15, 1985 at CFHT are analyzed. The classification of blazars into BL Lac objects and optically violently variable quasars is examined. The analysis reveals that for PKS 2208-137 the blazars have symmetric double radio lobes, the redshift is 0.392 + or - 0.002, the lobe power is 2.7 x 10 to the 33rd erg/s Hz, the linear size is 59 kpc, and the H-beta luminosity is 2 x 20 to the 43rd erg/sq cm s. For MC3 2032 + 107 the redshfit is calculated as 0.601 + or - 0.001, the asymmetrical radio halo power is 3.1 x 10 to the 32 erg/s Hz at 1.5 GHz, the linear size is 27 kpc, and the H-beta luminosity is about 10 to the 43 erg/s. 22 references.

Effects of dust on the infrared emission, selected line ratios, and polarization of Seyfert 1 galaxies, broad-line radio galaxies, and quasars

view Abstract Citations (66) References (87) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Effects of dust on the infrared emission, selected line ratios, and polarization of Seyfert 1 galaxies, broad-line radio galaxies, and quasars. Rudy, R. J. Abstract The results of an investigation of the effects of dust on several different types of emission and selected line ratios in active extra galactic objects are presented. Observational data from the literature are compared which determine the effect of dust on infrared emissions; the Balmer decrement; line ratios for the forbidden line of O III and H-beta; H-beta luminosities; and optical polarization. The objects observed included a number of Seyfert 1 galaxies, broad-line radio galaxies, and quasars. A compilation of the data is provided in the form of a table. It is found that optical surveys currently have a bias against objects with significant dust extinction, and that this bias becomes more pronounced with each redshift. Hot-dust associated with the gas from narrowline regions contributes significantly to the mid infrared flux in the luminosity of extragalactic quasars at 10 microns and in the forbidden line of O III. An inverse correlation was found in the line ratio of forbidden line of O III/H-beta and H-beta luminosity in broad-line radio galaxies. No correlation was found between optical polarization and the Balmer decrement in extragalactic active sources. For the vast majority of Seyfert galaxies extinction by dust in the plane of the hot galaxy has only a slight effect on the optical polarization, Balmer decrement and line ratio forbidden line-O III/H-beta. Publication: The Astrophysical Journal Pub Date: September 1984 DOI: 10.1086/162381 Bibcode: 1984ApJ...284...33R Keywords: Cosmic Dust; Infrared Spectra; Optical Polarization; Radio Galaxies; Seyfert Galaxies; Spectral Line Width; Balmer Series; Emission Spectra; Forbidden Transitions; Infrared Astronomy; Interstellar Extinction; Quasars; Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (148) NED (128)

Star formation in blue galaxies. I - Ultraviolet, optical, and infrared observations of NGC 4214 and NGC 4670

NGC 4214 and NGC 4760 have been observed between 1150 A and 1950 A with the IUE satellite, and new infrared and optical broad-band photometry have been obtained. The spectra of both galaxies are dominated by O stars, and, in the spectrum of NGC 4214, the C IV 1550 A line exhibits a P Cygni profile indicative of hot stars with large mass-loss rates. Although the optical spectra of both galaxies are dominated by strong narrow emission lines, no strong emission lines are seen in the UV (the observed Ly-alpha flux is dominated by geocoronal emission). Both galaxies contain giant H II region complexes in which the energy (in particular, the H-beta luminosity and the ultraviolet continuum) is provided by several hundred O stars. The comparison of the observed UVOIR energy distributions with evolutionary population models indicates that the regions observed consist of young 'bursts' of star formation superposed on an underlying old population. The initial mass function for this epoch of star formation is constrained to be similar in slope to or flatter than the Salpeter function.

DATA ON AN UNUSUAL WOLF-RAYET STAR IN THE NEARBY GALAXY IC 1613

ABSTRACT Observations of an H II region in IC 1613 which is excited by a hot Wolf-Rayet star are reported, and the nebular and stellar spectra are discussed. The nebular helium abundance is not far above the primordial value, while oxygen and argon are less abundant than in the sun or the Orion nebula by factors of about ten. The observed H-beta flux, corrected for interstellar extinction, corresponds to an H-beta luminosity of about 1.35 x 10 to the 36th ergs/s. The spectrum of the star shows broad C IV features reported by previous authors, and somewhat less broad O VI features. The nebular recombination lines can be used to make Zanstra-style estimates of the star's ionizing continuum. Most of this luminosity is probably at wavelengths similar to the peak of a 110,000 K blackbody spectrum. The Wolf-Rayet star is likely to have had a metal-poor initial composition.

X-ray, optical, and radio properties of quasars

view Abstract Citations (63) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS X-ray, optical, and radio properties of quasars. Blumenthal, G. R. ; Keel, W. C. ; Miller, J. S. Abstract A sample of 26 low-redshift quasars was examined for relationships between X-ray luminosity and optical spectroscopic features; all quasars were observed with the Einstein Observatory and with the IDS on the Lick 3 meter telescope. Evidence is found for correlations between quasar X-ray luminosity and both optical continuum luminosity and H-beta luminosity. In the latter case, there is a smooth relationship connecting quasars, Seyfert 1, and Seyfert 2 galaxies. For the quasars in this sample, there is also a strong correlation between optical continuum luminosity and both the H-beta luminosity and equivalent width. Evidence is also found for a weak correlation between alpha-prime (ox), the mean continuum spectral index between 5000 A and 2 keV, and Fe II equivalent width, H-beta equivalent width, H-beta line width at zero intensity, and the ratio of H-beta equivalent width to its line width at zero intensity. Publication: The Astrophysical Journal Pub Date: June 1982 DOI: 10.1086/160007 Bibcode: 1982ApJ...257..499B Keywords: Astronomical Spectroscopy; Luminosity; Quasars; Radio Spectra; Red Shift; X Ray Sources; Emission Spectra; Galactic Nuclei; H Beta Line; Light Emission; Seyfert Galaxies; Spectral Line Width; Astrophysics full text sources ADS | data products SIMBAD (26) NED (24)