Past-averaged Star Formation Rates Research Articles

EXPLORING SYSTEMATIC EFFECTS IN THE RELATION BETWEEN STELLAR MASS, GAS PHASE METALLICITY, AND STAR FORMATION RATE

ABSTRACT There is evidence that the well-established mass–metallicity relation in galaxies is correlated with a third parameter: star formation rate (SFR). The strength of this correlation may be used to disentangle the relative importance of different physical processes (e.g., infall of pristine gas, metal-enriched outflows) in governing chemical evolution. However, all three parameters are susceptible to biases that might affect the observed strength of the relation between them. We analyze possible sources of systematic error, including sample bias, application of signal-to-noise ratio cuts on emission lines, choice of metallicity calibration, uncertainty in stellar mass determination, aperture effects, and dust. We present the first analysis of the relation between stellar mass, gas phase metallicity, and SFR using strong line abundance diagnostics from Dopita et al. for ∼130,000 star-forming galaxies in the Sloan Digital Sky Survey and provide a detailed comparison of these diagnostics in an appendix. Using these new abundance diagnostics yields a 30%–55% weaker anti-correlation between metallicity and SFR at fixed stellar mass than that reported by Mannucci et al. We find that, for all abundance diagnostics, the anti-correlation with SFR is stronger for the relatively few galaxies whose current SFRs are elevated above their past average SFRs. This is also true for the new abundance diagnostic of Dopita et al., which gives anti-correlation between Z and SFR only in the high specific star formation rate (sSFR) regime, in contrast to the recent results of Kashino et al. The poorly constrained strength of the relation between stellar mass, metallicity, and SFR must be carefully accounted for in theoretical studies of chemical evolution.

GRADIENTS OF STELLAR POPULATION PROPERTIES AND EVOLUTION CLUES IN A NEARBY GALAXY M101

Multi-band photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of a nearby Scd type galaxy M 101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation, and star formation timescale in the form of the Sandage star formation history are obtained. When fitting with the models, we use the IRX-$A_\mathrm{FUV}$ relation, found to depend on a second parameter of birth rate b (ratio of present and past-averaged star formation rate), to constrain the dust attenuation. There are obvious parameter gradients in the disk of M101, which supports the theory of an "inside-out disk" growth scenario. Two distinct disc regions with different gradients of age and color are discovered, similar to another late-type galaxy NGC 628. The metallicity gradient of the stellar content is flatter than that of H {\sc ii} regions. The stellar disk is optically thicker inside than outside and the global dust attenuation of this galaxy is lower, compared with galaxies of similar and earlier morphological type. We highlight that a variational star formation timescale describes the real star formation history of a galaxy. The timescale increases steadily from the center to the outskirt. We also confirm that the bulge in this galaxy is a disk-like pseudobulge, whose evolution is likely to be induced by some secular processes of the small bar with relatively young age, rich metal, and much dust.

THE SINS SURVEY: SINFONI INTEGRAL FIELD SPECTROSCOPY OFz∼ 2 STAR-FORMING GALAXIES

We present the Spectroscopic Imaging survey in the near-infrared (near-IR) with SINFONI (SINS) of high-redshift galaxies. With 80 objects observed and 63 detected in at least one rest-frame optical nebular emission line, mainly Hα, represents the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z ~ 1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the SINS Hα sample, consisting of 62 rest-UV/optically selected sources at 1.3 < z < 2.6 for which we targeted primarily the Hα and [N II] emission lines. Only ≈30% of this sample had previous near-IR spectroscopic observations. The galaxies were drawn from various imaging surveys with different photometric criteria; as a whole, the Hα sample covers a reasonable representation of massive M_* ≳ 10^(10) M_☉ star-forming galaxies at z ≈ 1.5-2.5, with some bias toward bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans 2 orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values ≈3 × 10^(10) M_☉, ≈70 M_☉ yr^(–1), and ≈3 Gyr^(–1). The ionized gas distribution and kinematics are spatially resolved on scales ranging from ≈1.5 kpc for adaptive optics assisted observations to typically ≈4-5 kpc for seeing-limited data. The Hα morphologies tend to be irregular and/or clumpy. About one-third of the Hα sample galaxies are rotation-dominated yet turbulent disks, another one-third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The Hα luminosities and equivalent widths suggest on average roughly twice higher dust attenuation toward the H II regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates.

AN ULTRA-DEEP NEAR-INFRARED SPECTRUM OF A COMPACT QUIESCENT GALAXY ATz= 2.2

Several recent studies have shown that about half of the massive galaxies at z~2 are in a quiescent phase. Moreover, these galaxies are commonly found to be ultra-compact with half-light radii of ~1 kpc. We have obtained a ~29 hr spectrum of a typical quiescent, ultra-dense galaxy at z=2.1865 with the Gemini Near-Infrared Spectrograph. The spectrum exhibits a strong optical break and several absorption features, which have not previously been detected in z>2 quiescent galaxies. Comparison of the spectral energy distribution with stellar population synthesis models implies a low star formation rate (SFR) of 1-3 Msol/yr, an age of 1.3-2.2 Gyr, and a stellar mass of ~2x10^11 Msol. We detect several faint emission lines, with emission-line ratios of [NII]/Halpha, [SII]/Halpha and [OII]/[OIII] typical of low-ionization nuclear emission-line regions. Thus, neither the stellar continuum nor the nebular emission implies active star formation. The current SFR is <1% of the past average SFR. If this galaxy is representative of compact quiescent galaxies beyond z=2, it implies that quenching of star formation is extremely efficient and also indicates that low luminosity active galactic nuclei (AGNs) could be common in these objects. Nuclear emission is a potential concern for the size measurement. However, we show that the AGN contributes <8% to the rest-frame optical emission. A possible post-starburst population may affect size measurements more strongly; although a 0.5 Gyr old stellar population can make up <10% of the total stellar mass, it could account for up to ~40% of the optical light. Nevertheless, this spectrum shows that this compact galaxy is dominated by an evolved stellar population.

The UV‐Optical Galaxy Color‐Magnitude Diagram. I. Basic Properties

We have analyzed the bivariate distribution of galaxies as a function of ultraviolet-optical colors and absolute magnitudes in the local universe. The sample consists of galaxies with redshifts and optical photometry from the Sloan Digital Sky Survey (SDSS) main galaxy sample matched with detections in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands in the Medium Imaging Survey being carried out by the Galaxy Evolution Explorer (GALEX) satellite. In the (NUV − r)_(0.1) versus M_(r,0.1) galaxy color-magnitude diagram, the galaxies separate into two well-defined blue and red sequences. The (NUV − r)_(0.1) color distribution at each M_(r,0.1) is not well fit by the sum of two Gaussians due to an excess of galaxies in between the two sequences. The peaks of both sequences become redder with increasing luminosity, with a distinct blue peak visible up to M_(r,0.1) ~ − 23. The r_(0.1)-band luminosity functions vary systematically with color, with the faint-end slope and characteristic luminosity gradually increasing with color. After correcting for attenuation due to dust, we find that approximately one-quarter of the color variation along the blue sequence is due to dust, with the remainder due to star formation history and metallicity. Finally, we present the distribution of galaxies as a function of specific star formation rate and stellar mass. The specific star formation rates imply that galaxies along the blue sequence progress from low-mass galaxies with star formation rates that increase somewhat with time to more massive galaxies with a more or less constant star formation rate. Above a stellar mass of ~10^(10.5) M_☉, galaxies with low ratios of current to past averaged star formation rate begin to dominate.

Evolutionary Implications from SDSS J085338.27+033246.1: A Spectacular Narrow‐Line Seyfert 1 Galaxy with Young Poststarburst

We analyze the physical properties of the poststarburst active galactic nucleus (AGN) SDSS J085338.27+033246.1 according to its optical spectrum and discuss its implications on AGNs' evolution. The spectra principal component analysis (PCA) method is developed to extract emission lines and absorption features from the total light spectrum. The emission-line analysis indicates that the object can be classified as a narrow-line Seyfert 1 galaxy with Fe /HβB = 2.4 ± 0.2, large Eddington ratio (~0.34), small black hole mass (~1.1 × 107 M☉), and intermediately strong radio emission. A simple single stellar population model indicates that the absorption features are rather well reproduced by a ~100 Myr old starburst with a mass of ~7 × 109 M☉. However, the current star formation rate, ~3.0 M☉ yr-1, inferred from the [O II] emission is much smaller than the past average star formation rate, ~70 M☉ yr-1. The line ratio diagnosis using Baldwin-Phillips-Terlevich (BPT) diagrams indicates that the narrow emission lines are almost entirely emitted from H II regions. We further discuss a possible evolutionary path that links AGN and starburst phenomena.

Spitzer imaging of i′-drop galaxies: old stars at z≈ 6

We present new evidence for mature stellar populations with ages >100 Myr in massive galaxies (Mstellar > 1010 M⊙) seen at a time when the Universe was less than 1 Gyr old. We analyse the prominent detections of two z≈ 6 star-forming galaxies (SBM03#1 and #3) made at wavelengths corresponding to the rest-frame optical using the Infrared Array Camera camera onboard the Spitzer Space Telescope. We had previously identified these galaxies in Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) / Great Observatories Origins Deep Survey (GOODS) images of Chandra Deep Field South through the ‘i′-drop’ Lyman-break technique, and subsequently confirmed the identification spectroscopically with the Keck telescope. The new Spitzer photometry reveals significant Balmer/4000-A discontinuities, indicative of dominant stellar populations with ages >100 Myr. Fitting a range of population synthesis models (for normal initial mass functions) to the HST/Spitzer photometry yields ages of 250–650 Myr and implied formation redshifts zf≈ 7.5–13.5 in presently-accepted world models. Remarkably, our sources have best-fitting stellar masses of 1.3–3.8 × 1010 M⊙ (95 per cent confidence) assuming a Salpeter IMF. This indicates that at least some galaxies with stellar masses >20 per cent of those of a present-day L* galaxy had already assembled within the first Gyr after the Big Bang. We also deduce that the past average star formation rate must be comparable to the current observed rate (SFRUV~5–30 M⊙ yr−1), suggesting that there may have been more vigorous episodes of star formation in such systems at higher redshifts. Although a small sample, limited primarily by Spitzer's detection efficiency, our result lends support to the hypothesis advocated in our earlier analyses of the Ultra Deep Field and GOODS HST/ACS data. The presence of established systems at z≈ 6 suggests that long-lived sources at earlier epochs (z > 7) played a key role in reionizing the Universe.

Toward an Understanding of the Rapid Decline of the Cosmic Star Formation Rate

We present a first analysis of deep 24 μm observations with the Spitzer Space Telescope of a sample of nearly 1500 galaxies in a thin redshift slice, 0.65 ≤ z < 0.75. We combine the infrared data with redshifts, rest-frame luminosities, and colors from COMBO-17 and with morphologies from Hubble Space Telescope images collected by the Galaxy Evolution from Morphology and SEDs (GEMS) and Great Observatories Origins Deep Survey (GOODS) projects. To characterize the decline in star formation rate (SFR) since z ~ 0.7, we estimate the total thermal IR luminosities, SFRs, and stellar masses for the galaxies in this sample. At z ~ 0.7, nearly 40% of intermediate- and high-mass galaxies (with stellar masses ≥2 × 1010 M☉) are undergoing a period of intense star formation above their past-averaged SFR. In contrast, less than 1% of equally massive galaxies in the local universe have similarly intense star formation activity. Morphologically undisturbed galaxies dominate the total infrared luminosity density and SFR density: at z ~ 0.7, more than half of the intensely star-forming galaxies have spiral morphologies, whereas less than ~30% are strongly interacting. Thus, a decline in major merger rate is not the underlying cause of the rapid decline in cosmic SFR since z ~ 0.7. Physical properties that do not strongly affect galaxy morphology—for example, gas consumption and weak interactions with small satellite galaxies—appear to be responsible.

The physical properties of star-forming galaxies in the low-redshift Universe

Abstract We present a comprehensive study of the physical properties of ∼ 105 galaxies with measurable star formation in the Sloan Digital Sky Survey (SDSS). By comparing physical information extracted from the emission lines with continuum properties, we build up a picture of the nature of star-forming galaxies at z &amp;lt; 0.2. We develop a method for aperture correction using resolved imaging and show that our method takes out essentially all aperture bias in the star formation rate (SFR) estimates, allowing an accurate estimate of the total SFRs in galaxies. We determine the SFR density to be 1.915+0.02−0.01 (random)+0.14−0.42 (systematic) h7010−2 M⊙ yr−1 Mpc−3 at z= 0.1 (for a Kroupa initial mass function) and we study the distribution of star formation as a function of various physical parameters. The majority of the star formation in the low-redshift Universe takes place in moderately massive galaxies (1010–1011 M⊙), typically in high surface brightness disc galaxies. Roughly 15 per cent of all star formation takes place in galaxies that show some sign of an active nucleus. About 20 per cent occurs in starburst galaxies. By focusing on the SFR per unit mass we show that the present to past average SFR, the Scalo b-parameter, is almost constant over almost three orders of magnitude in mass, declining only at M* &amp;gt; 1010 M⊙. The volume averaged b parameter is 0.408+0.005−0.002 (random)+0.029−0.090 (systematic)h−170. We use this value to constrain the star formation history of the Universe. For the concordance cosmology the present-day Universe is forming stars at at least 1/3 of its past average rate. For an exponentially declining cosmic star formation history this corresponds to a time-scale of 7+0.7−1.5 Gyr. In agreement with other work we find a correlation between b and morphological type, as well as a tight correlation between the 4000-Å break (D4000) and b. We discuss how D4000 can be used to estimate b parameters for high-redshift galaxies.

Star formation history and dust content of galaxies drawn from ultraviolet surveys

We compile a new sample of 115 nearby, non-Seyfert galaxies spanning a wide range of star formation activities, from starburst to nearly dormant, based on ultraviolet observations with various satellites. We combine these observations with infrared observations to study the relation between ratio of total far-infrared to ultraviolet luminosity and ultraviolet spectral slope (the IRX-UV relation). We show that, at fixed ultraviolet spectral slope, quiescent star-forming galaxies in our sample have systematically lower ratio of total far-infrared to ultraviolet luminosity than starburst galaxies. The strengths of spectral indices sensitive to star formation history, such as the 4000-A spectral discontinuity and the Ha emission equivalent width, correlate well with distance from the mean relation for starburst galaxies in the IRX-UV diagram, while there is little or no correlation between the dust-sensitive Hα/Hβ ratio and this distance. This is strong observational evidence that the star formation history is relevant to the second parameter affecting the IRX-UV relation. We show that these results can be understood in the framework of the simple model of Charlot & Fall for the transfer of starlight through the interstellar medium in galaxies. We confirm that, for starburst galaxies, the tight IRX-UV relation can be understood most simply as a sequence in overall dust content. In addition, we find that the broadening of the relation for quiescent star-forming galaxies can be understood most simply as a sequence in the ratio of present to past-averaged star formation rate. We use a library of Monte Carlo realizations of galaxies with different star formation histories and dust contents to quantify the accuracy to which the ultraviolet attenuation A FUV of a galaxy can be estimated from either the ratio of far-infrared to ultraviolet luminosity or the ultraviolet spectral slope. We provide simple formulae for estimating A FUV as a function of either of these observational quantities and show that the accuracy of these estimates can be significantly improved if some constraints are available on the ratio of present to past-averaged star formation rate.

Evolution of spiral galaxies. 2: The star formation history in the solar neighborhood

view Abstract Citations (28) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolution of Spiral Galaxies. II. The Star Formation History in the Solar Neighborhood Pardi, Maria Chiara ; Ferrini, Federico Abstract This paper extends the discussion about the evolution of stellar populations in the solar vicinity, begun with the paper of Ferrini et al. (1992) where our new model of the evolution of spirals was presented in detail. We compare model predictions obtained under different assumptions about the halo collapse timescale, star formation efficiency, and initial mass function, with a wide set of observational constraints which need simultaneous fulfillment; halo-to-disk mass ratio, disk gas fraction, present star formation rate, Type I and II supernova rates, enrichment time for a number of chemical elements, age-metallicity relation, G dwarf distribution, and present-day mass function. From this comparison we draw the following conclusions: 1. The star formation rate in the solar neighborhood had to rise slowly, on a timescale of about 2 Gyr, and its maximum was not greater than about 10 times the present value nor less than about 3 times, and the ratio of the past average star formation rate to the present rate in our preferred model solution is {PSI}^bar^/{PSI}(now)~5; this value depends on the initial mass function and on the assumed Galactic age. 2. The above-mentioned star formation history is obtained only if the disk formed from the halo with a long timescale (>= 5 Gyr). Such a request conflicts with halo observational properties, which seem to be fulfilled better by a quicker collapse (<= 2 Gyr). We suggest that this contradiction could be overcome allowing for a thick disk phase during the collapse. 3. Focusing the analysis on the differences in production timescale and enrichment history of different chemical elements, we can place some limits on the initial mass function. The model therefore constitutes a test for such functions, and we favor the one proposed by Ferrini, Palla, & Penco (1990). Publication: The Astrophysical Journal Pub Date: February 1994 DOI: 10.1086/173666 Bibcode: 1994ApJ...421..491P Keywords: Astronomical Models; Galactic Evolution; Solar Neighborhood; Spiral Galaxies; Star Formation; Mathematical Models; Stellar Composition; Stellar Evolution; Supernovae; Astrophysics; GALAXIES: SPIRAL; GALAXY: EVOLUTION; GALAXY: STELLAR CONTENT; STARS: FORMATION full text sources ADS | Related Materials (6) Part 1: 1992ApJ...387..138F Part 3: 1994ApJ...427..745F Part 4: 1995ApJ...444..207P Part 5: 1995ApJ...454..726M Part 6: 1996ApJ...466..668M Part 7: 1997ApJ...475..519M