The escape fraction of ionizing photons from galaxies is a crucial quantity controlling the cosmic ionizing background radiation and the reionization. Various estimates of this parameter can be ...obtained in the redshift range z= 0–6, either from direct observations or from the observed ionizing background intensities. We compare them homogeneously in terms of the observed flux density ratio of ionizing (∼900 Å rest-frame) to non-ionizing ultraviolet (∼1500 Å rest-frame) corrected for the intergalactic absorption. The escape fraction is found to increase by an order of magnitude, from a value less than 0.01 at z ≲ 1 to about 0.1 at z ≳ 4.
Gas flows in and out of galaxies are one of the key unknowns in today's galaxy evolution studies. Because gas flows carry mass, energy, and metals, they are believed to be closely connected to the ...star formation history of galaxies. Most of these processes take place in the circum-galactic medium (CGM) which remains challenging to observe in emission. A powerful tool to study the CGM gas is offered by combining observations of the gas traced by absorption lines in quasar spectra with detection of the stellar component of the same absorbing-galaxy. To this end, we have targeted the z sub( abs) = 1.825 sub-damped Ly... absorber (sub-DLA) towards the z sub( em) = 2.102 quasar 2dF J 223941.8-294955 (hereafter Q 2239-2949) with the ESO VLT/X-Shooter spectrograph. Our aim is to investigate the relation between its properties in emission and in absorption. The derived metallicity of the sub-DLA with log N(H i) = 19.84 plus or minus 0.14 cm super( -2) is M/H > -0.75. Using the Voigt profile optical depth method, we measure ...(Fe ii) = 64 km s super( -1). The sub-DLA galaxy counterpart is located at an impact parameter of 2...4 plus or minus 0...2 (20.8 plus or minus 1.7 kpc at z = 1.825). We have detected Ly... and marginal Oii emissions. The mean measured flux of the Ly... line is F... ~ 5.7 x 10 super( -18) erg s super( -1) cm super( -2) A super( -1), corresponding to a dust uncorrected SFR of ~0.13 M... yr super( -1). (ProQuest: ... denotes formulae/symbols omitted.)
We have used the GALEX (Galaxy Evolution Explorer) spectroscopic survey mode, with a resolution of image8 Aa in the far-ultraviolet (FUV; 1350-1750 Aa) and image20 Aa in the near-ultraviolet (NUV; ...1950-2750 Aa) for a systematic search of Ly alpha -emitting galaxies at low redshift. Our aim is to fill a gap between high-redshift surveys and a small set of objects studied in detail in the nearby universe. A blind search of 7018 spectra extracted in five deep exposures (5.65 deg super(2)) has resulted in 96 Ly alpha - emitting galaxy candidates in the FUV domain after accounting for broad-line AGNs. The Ly alpha equivalent widths (EWs) are consistent with stellar population model predictions and show no trends as a function of UV color or UV luminosity, with the exception of a possible decrease in the most luminous objects that may be due to small-number statistics. The objects' distribution in EW is similar to that at image, but their fraction among star-forming galaxies is smaller. Avoiding uncertain candidates, a subsample of 66 objects in the range image has been used to build a Ly alpha luminosity function (LF). The incompleteness due to objects with significant Ly alpha emission but a UV continuum too low for spectral extraction has been evaluated. A comparison with H alpha LFs in the same redshift domain is consistent with an average Ly alpha /H alpha of image1 in about 15% of the star-forming galaxies. A comparison with high-redshift Ly alpha LFs implies an increase of the Ly alpha luminosity density by a factor of about 16 from image to image. By comparison with the factor of 5 increase in the UV luminosity density in the same redshift range, this suggests an increase of the average Ly alpha escape fraction with redshift.
We use GALEX/optical photometry to construct color-color relationships for early-type galaxies sorted by morphological type. We have matched objects in the GALEX GR1 public release and the first ...IR1.1 internal release, with the RC3 early-type galaxies having a morphological type -5.5 less than or equal to T < -1.5, with mean error on T < 1.5 and mean error on (B - V) sub(T) < 0.05. After visual inspection of each match, we are left with 130 galaxies with reliable GALEX pipeline photometry in the far-UV and near-UV bands. This sample is divided into ellipticals (-5.5 less than or equal to T < -3.5) and lenticulars (-3.5 less than or equal to T < -1.5). After correction for Galactic extinction, the color-color diagrams FUV - NUV versus (B - V) sub(To) are plotted for the two subsamples. We find a tight anticorrelation between the FUV - NUV and (B - V) sub(To) colors for ellipticals, with the UV color getting bluer when the (B - V) sub(To) gets redder. This relationship very likely is an extension of the color-metallicity relationship in the GALEX NUV band. We suspect that the main source of the correlation is metal line blanketing in the NUV band. The FUV - NUV versus B - V correlation has larger scatter for lenticular galaxies; we speculate that this reflects the presence of low-level star formation. If the latter objects (i.e., those that are blue both in FUV - NUV and in B - V) are interpreted as harboring recent star formation activity, this would be the case for a few percent ( similar to 4%) of ellipticals and similar to 15% of lenticulars; this would mean about 10% of early-type galaxies have residual star formation in our full sample of 130 early-type galaxies. We also plot FUV - NUV versus the Mg2 index and central velocity dispersion. We find a tight anticorrelation between FUV - NUV and the Mg2 index; we suspect that this reflects blanketing in the NUV band being correlated with overall metallicity. We find a marginal anticorrelation of FUV - V sub(T) with Mg2 for elliptical galaxies.
We present the GALEX UV photometry of the elliptical galaxies in Abell clusters at moderate redshifts (z < 0.2) for the study of the look-back time evolution of the UV upturn phenomenon. The ...brightest elliptical galaxies (M sub(r) unk -22) in 12 remote clusters are compared with the nearby giant elliptical galaxies of comparable optical luminosity in the Fornax and Virgo clusters. The sample galaxies presented here appear to be quiescent without signs of massive star formation or strong nuclear activity and show smooth, extended profiles in their UV images, indicating that the far-UV (FUV) light is mostly produced by hot stars in the underlying old stellar population. Compared to their counterparts in nearby clusters, the FUV flux of cluster giant elliptical galaxies at moderate redshifts fades rapidly with similar to 2 Gyr of look-back time, and the observed pace in FUV - V color evolution agrees reasonably well with the prediction from the population synthesis models where the dominant FUV source is hot horizontal-branch stars and their progeny. A similar amount of color spread ( similar to 1 mag) in FUV - V exists among the brightest cluster elliptical galaxies at z similar to 0.1, as observed among the nearby giant elliptical galaxies of comparable optical luminosity.
This contribution gathers the contents of the white paper submitted by the UV community to the Call issued by the European Space Agency in March 2013, for the definition of the L2 and L3 missions in ...the ESA science program. We outlined the key science that a large UV facility would make possible and the instrumentation to be implemented.
The growth of luminous structures and the building blocks of life in the Universe began as primordial gas was processed in stars and mixed at galactic scales. The mechanisms responsible for this development are not well-understood and have changed over the intervening 13 billion years. To follow the evolution of matter over cosmic time, it is necessary to study the strongest (resonance) transitions of the most abundant species in the Universe. Most of them are in the ultraviolet (UV; 950 Å–3000 Å) spectral range that is unobservable from the ground. A versatile space observatory with UV sensitivity a factor of 50–100 greater than existing facilities will revolutionize our understanding of the Universe.
Habitable planets grow in protostellar discs under ultraviolet irradiation, a by-product of the star-disk interaction that drives the physical and chemical evolution of discs and young planetary systems. The electronic transitions of the most abundant molecules are pumped by this UV field, providing unique diagnostics of the planet-forming environment that cannot be accessed from the ground. Earth’s atmosphere is in constant interaction with the interplanetary medium and the solar UV radiation field. A 50–100 times improvement in sensitivity would enable the observation of the key atmospheric ingredients of Earth-like exoplanets (carbon, oxygen, ozone), provide crucial input for models of biologically active worlds outside the solar system, and provide the phenomenological baseline to understand the Earth atmosphere in context.
Gas flows in and out of galaxies are one of the key unknowns in today's galaxy evolution studies. Because gas flows carry mass, energy, and metals, they are believed to be closely connected to the ...star formation history of galaxies. Most of these processes take place in the circum-galactic medium (CGM) which remains challenging to observe in emission. A powerful tool to study the CGM gas is offered by combining observations of the gas traced by absorption lines in quasar spectra with detection of the stellar component of the same absorbing-galaxy. To this end, we have targeted the z^sub abs^ = 1.825 sub-damped Ly... absorber (sub-DLA) towards the z^sub em^ = 2.102 quasar 2dF J 223941.8-294955 (hereafter Q 2239-2949) with the ESO VLT/X-Shooter spectrograph. Our aim is to investigate the relation between its properties in emission and in absorption. The derived metallicity of the sub-DLA with log N(H i) = 19.84 ± 0.14 cm^sup -2^ is M/H > -0.75. Using the Voigt profile optical depth method, we measure ...(Fe ii) = 64 km s^sup -1^. The sub-DLA galaxy counterpart is located at an impact parameter of 2...4 ± 0...2 (20.8 ± 1.7 kpc at z = 1.825). We have detected Ly... and marginal O ii emissions. The mean measured flux of the Ly... line is F... ~ 5.7 x 10^sup -18^ erg s^sup -1^ cm^sup -2^ A^sup -1^, corresponding to a dust uncorrected SFR of ~0.13 M... yr^sup -1^. (ProQuest: ... denotes formulae/symbols omitted.)
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