UV Star Formation Rates in the Local Universe (original) (raw)
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The ultraviolet and infrared star formation rates of compact group galaxies: an expanded sample
Monthly Notices of the Royal Astronomical Society, 2016
Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended time-scales. We expand the census of star formation in compact group galaxies by and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 µm photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFR UV ) using the UVOT uvw2 photometry. Similarly, we use the MIPS 24 µm photometry to estimate the component of the SFR that is obscured by dust (SFR IR ). We find that galaxies which are MIR-active (MIR-'red'), also have bluer UV colours, higher specific SFRs, and tend to lie in H I-rich groups, while galaxies that are MIR-inactive (MIR-'blue') have redder UV colours, lower specific SFRs, and tend to lie in H I-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M yr −1 , indicating this might be the most common value in compact groups. In contrast, the specific SFR distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific SFR is the best tracer of gas depletion and galaxy evolution in compact groups.
The Astrophysical Journal, 2011
We investigate the average physical properties and star formation histories (SFHs) of the most UV-luminous star-forming galaxies at z ∼ 3.7. Our results are based on the average spectral energy distributions (SEDs), constructed from stacked optical to infrared photometry, of a sample of the 1,913 most UV-luminous star-forming galaxies found in 5.3 square degrees of the NOAO Deep Wide-Field Survey. We find that the shape of the average SED in the rest-optical and infrared is fairly constant with UV luminosity: i.e., more UV luminous galaxies are, on average, also more luminous at longer wavelengths. In the rest-UV, however, the spectral slope β (≡ dlogF λ /dlogλ; measured at 0.13µm < λ rest < 0.28µm) rises steeply with the median UV luminosity from −1.8 at L ≈ L * to −1.2 (L ≈ 4 − 5L *). We use population synthesis analyses to derive their average physical properties and find that: (1) L UV , and thus star-formation rates (SFRs), scale closely with stellar mass such that more UV-luminous galaxies are more massive; (2) The median ages indicate that the stellar populations are relatively young (200-400 Myr) and show little correlation with UV luminosity; and (3) More UVluminous galaxies are dustier than their less-luminous counterparts, such that L ≈ 4 − 5L * galaxies are extincted up to A(1600) = 2 mag while L ≈ L * galaxies have A(1600) = 0.7 − 1.5 mag. We argue that the average SFHs of UV-luminous galaxies are better described by models in which SFR increases with time in order to simultaneously reproduce the tight correlation between the UV-derived SFR and stellar mass, and their universally young ages. We demonstrate the potential of measurements of the SFR-M * relation at multiple redshifts to discriminate between simple models of SFHs. Finally, we discuss the fate of these UV-brightest galaxies in the next 1 − 2 Gyr and their possible connection to the most massive galaxies at z ∼ 2.
Hα and UV luminosities and star formation rates in a large sample of luminous compact galaxies
Astrophysics and Space Science, 2013
We present the results of a statistical study of the star formation rates (SFR) derived from the Galaxy Evolution Explorer (GALEX) observations in the ultraviolet continuum and in the Hα emission line for a sample of about 800 luminous compact galaxies (LCGs). Galaxies in this sample have a compact structure and include one or several regions of active star formation. Global galaxy characteristics (metallicity, luminosity, stellar mass) are intermediate between ones of the nearby blue compact dwarf (BCD) galaxies and Lyman-break galaxies (LBGs) at high redshifts z > 2 -3. SFRs were corrected for interstellar extinction which was derived from the optical Sloan Digital Sky Survey (SDSS) spectra. We find that SFRs derived from the galaxy luminosities in the far ultraviolet (FUV) and near ultraviolet (NUV) ranges vary in a wide range from 0.18 M ⊙ yr −1 to 113 M ⊙ yr −1 with median values of 3.8 M ⊙ yr −1 and 5.2 M ⊙ yr −1 , respectively. Simple regression relations are found for luminosities L(Hα) and L(UV) as functions of the mass of the young stellar population, the starburst age, and the galaxy metallicity. We consider the evolution of L(Hα), L(FUV) and L(NUV) with a starburst age and introduce new characteristics of star formation, namely the initial Hα, FUV and NUV luminosities at zero starburst age.
Star formation in the nearby universe: the ultraviolet and infrared points of view
HAL (Le Centre pour la Communication Scientifique Directe), 2006
This work presents the main ultraviolet (UV) and far-infrared (FIR) properties of two samples of nearby galaxies selected from the GALEX (k ¼ 2315 8, hereafter NUV) and IRAS (k ¼ 60 m) surveys, respectively. They are built in order to obtain detection at both wavelengths for most of the galaxies. Star formation rate (SFR) estimators based on the UV and FIR emissions are compared. Systematic differences are found between the SFR estimators for individual galaxies based on the NUV fluxes corrected for dust attenuation and on the total IR luminosity. A combined estimator based on NUV and IR luminosities seems to be the best proxy over the whole range of values of SFR. Although both samples present similar average values of the birthrate parameter b, their star-formation-related properties are substantially different: NUV-selected galaxies tend to show larger values of b for lower masses, SFRs, and dust attenuation, supporting previous scenarios of star formation history (SFH). Conversely, about 20% of the FIR-selected galaxies show high values of b, SFR, and NUVattenuation. These galaxies, most of them being LIRGs and ULIRGs, break down the downsizing picture of SFH; however, their relative contribution per unit volume is small in the local universe. Finally, the cosmic SFR density of the local universe is estimated in a consistent way from the NUVand IR luminosities.
Monthly Notices of the Royal Astronomical Society, 2012
The observed ultraviolet continuum (UVC) slope is potentially a powerful diagnostic of dust obscuration in star forming galaxies. However, the intrinsic slope is also sensitive to the form of the stellar initial mass function (IMF) and to the recent star formation and metal enrichment histories of a galaxy. Using the galform semi-analytical model of galaxy formation, we investigate the intrinsic distribution of UVC slopes. For star-forming galaxies, we find that the intrinsic distribution of UVC slopes at z = 0, parameterised by the power law index β, has a standard deviation of σ β ≃ 0.30. This suggests an uncertainty on the inferred UV attenuation of A fuv ≃ 0.7 (assuming a Calzetti attenuation curve) for an individual object, even with perfect photometry. Furthermore, we find that the intrinsic UVC slope correlates with star formation rate, intrinsic UV luminosity, stellar mass and redshift. These correlations have implications for the interpretation of trends in the observed UVC slope with these quantities irrespective of the sample size or quality of the photometry. Our results suggest that in some cases the attenuation by dust has been incorrectly estimated.
The Astrophysical Journal, 2010
We have measured the near-infrared colors and the fluxes of individual pixels in 68 galaxies common to the Spitzer Infrared Nearby Galaxies Survey and the Large Galaxy Atlas Survey. Each galaxy was separated into regions of increasingly red near-infrared colors. In the absence of dust extinction and other non-stellar emission, stellar populations are shown to have relatively constant NIR colors, independent of age. In regions of high star formation, the average intensity of pixels in red-excess regions (at 1.25 µm, 3.6 µm, 4.5 µm, 5.6 µm, 8.0 µm and 24 µm) scales linearly with the intrinsic intensity of Hα emission, and thus with the star-formation rate within the pixel. This suggests that most NIR-excess regions are not red because their light is being depleted by absorption. Instead, they are red because additional infrared light is being contributed by a process linked to star-formation. This is surprising because the shorter wavelength bands in our study (1.25 µm-5.6 µm) do not probe emission from cold (10-20 K) and warm (50-100 K) dust associated with star-formation in molecular clouds. However, emission from hot dust (700-1000 K) and/or Polycyclic Aromatic Hydrocarbon molecules can explain the additional emission seen at the shorter wavelengths in our study. The contribution from hot dust and/or PAH emission at 2 µm-5 µm and PAH emission at 5.6 µm and 8.0 µm scales linearly with warm dust emission at 24 µm and the intrinsic Hα emission. Since both are tied to the star-formation rate, our analysis shows that the NIR excess continuum emission and PAH emission at ∼ 1 − 8 µm can be added to spectral energy distribution models in a very straight-forward way, by simply adding an additional component to the models that scales linearly with star-formation rate. Recent work by and shows that a good estimator for the starformation rate emerges from the linear combination of a galaxy's near-UV or visible-wavelength emission (either UV continuum or line fluxes, attenuated by dust) and its
The infrared side of galaxy formation. I. The local universe in the semi-analytical framework
2000
We present a new evolutionary model for the far-UV to sub-mm properties of the galaxy population. This combines a semi-analytic galaxy formation model based on hierarchical clustering (GALFORM) with a spectro-photometric code which includes dust reprocessing (GRASIL). The former provides the star formation and metal enrichment histories, together with the gas mass and various geometrical parameters, for a representative sample of galaxies formed in different density environments. These quantities allow us to model the SEDs of galaxies, taking into account stellar emission and also dust extinction and re-emission. Two phases are considered for the dust: molecular cloud complexes, where stars are assumed to be born, and the diffuse interstellar medium. The model includes both galaxies forming stars quiescently in disks, and starbursts triggered by galaxy mergers. We test our models against the observed spectro-photometric properties of galaxies in the local Universe. The models reproduce fairly well the SEDs of normal spirals and starbursts, and their internal extinction properties. The starbursts follow the observed relationship between the FIR to UV luminosity ratio and the slope of the UV continuum. They also reproduce the observed starburst attenuation law (Calzetti et al 99). This result is remarkable, because we use a dust mixture which reproduces the Milky Way extinction law. It suggests that the observed attenuation law is related to the geometry of the stars and dust. We compute galaxy luminosity functions over our wide range of wavelengths, which turn out to be in good agreement with observational data. The UV continuum turns out to be a poor star formation indicator for our models, whilst the infrared luminosity is much more reliable.
2014
Aims. Our knowledge of the cosmic mass assembly relies on measurements of star formation rates (SFRs) and stellar masses (M star ), of galaxies as a function of redshift. These parameters must be estimated in a consistent way with a good knowledge of systematics before studying their correlation and the variation of the specific star formation rate. Constraining these fundamental properties of galaxies across the Universe is of utmost importance if we want to understand galaxy formation and evolution. Methods. We seek to derive star formation rates and stellar masses in distant galaxies and to quantify the main uncertainties affecting their measurement. We explore the impact of the assumptions made in their derivation with standard calibrations or through a fitting process, as well as the impact of the available data, focusing on the role of infrared (IR) emission originating from dust. Results. We build a sample of galaxies with z > 1, all observed from the ultraviolet to the infrared in their rest frame. The data are fitted with the code CIGALE, which is also used to build and analyse a catalogue of mock galaxies. Models with different star formation histories are introduced: an exponentially decreasing or increasing star formation rate and a more complex one coupling a decreasing star formation rate with a younger burst of constant star formation. We define different set of data, with or without a good sampling of the ultraviolet range, near-infrared, and thermal infrared data. Variations of the metallicity are also investigated. The impact of these different cases on the determination of stellar mass and star formation rate are analysed. Conclusions. Exponentially decreasing models with a redshift formation of the stellar population z f 8 cannot fit the data correctly. All the other models fit the data correctly at the price of unrealistically young ages when the age of the single stellar population is taken to be a free parameter, especially for the exponentially decreasing models. The best fits are obtained with two stellar populations. As long as one measurement of the dust emission continuum is available, SFR are robustly estimated whatever the chosen model is, including standard recipes. The stellar mass measurement is more subject to uncertainty, depending on the chosen model and the presence of near-infrared data, with an impact on the SFR-M star scatter plot. Conversely, when thermal infrared data from dust emission are missing, the uncertainty on SFR measurements largely exceeds that of stellar mass. Among all physical properties investigated here, the stellar ages are found to be the most difficult to constrain and this uncertainty acts as a second parameter in SFR measurements and as the most important parameter for stellar mass measurements.
The Astrophysical Journal, 2005
We investigate the nature of the diffuse intracluster ultraviolet light seen in 12 local starburst galaxies, using long-slit ultraviolet spectroscopy obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). We take this faint intracluster light to be the field in each galaxy and compare its spectroscopic signature with Starburst99 evolutionary synthesis models and with neighboring star clusters. Our main result is that the diffuse ultraviolet light in 11 of the 12 starbursts lacks the strong O star wind features that are clearly visible in spectra of luminous clusters in the same galaxies. The difference in stellar features dominating cluster and field spectra indicates that the field light comes primarily from a different stellar population and not from scattering of UV photons originating in the massive clusters. A cut along the spatial direction of the UV spectra establishes that the field light is not smooth but rather shows numerous ``bumps and wiggles.'' Roughly 30%-60% of these faint peaks seen in field regions of the closest (<4 Mpc) starbursts appear to be resolved, suggesting a contribution from superpositions of stars and/or faint star clusters. Complementary WFPC2 UVI imaging for the three nearest target galaxies, NGC 4214, NGC 4449, and NGC 5253, is used to obtain a broader picture and establish that all three galaxies have a dispersed population of unresolved, luminous blue sources. Because the field spectra are dominated by B stars, we suggest that the individual sources observed in the WFPC2 images are individual B stars (rather than O stars) or small star clusters. We consider several scenarios to understand the lack of observed massive stars in the field and their implications for the origin of the field stellar population. If the field stellar populations formed in situ, the field must have either an IMF that is steeper than Salpeter (α~-3.0 to -3.5) or a Salpeter slope with an upper mass cutoff of 30-50 Msolar. If star formation occurs primarily in star clusters, the field could be composed of older, faded clusters and/or a population that is coeval with the luminous clusters but lower in mass. We use these benchmark populations to place constraints on the field stellar population origin. Although the field probably includes stars of different ages, the UV light is dominated by the youngest stellar populations in the field. If the field is composed of older, dissolving clusters, we estimate that star clusters (regardless of mass) need to dissolve on timescales 7-10 Myr to create the field. If the field is composed of young clusters that fall below the detection limit of individual sources in our spectroscopy, they would have to be several hundred solar masses or less, in order to be deficient in O stars, despite their extreme youth. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.