- ID:
- ivo://CDS.VizieR/J/ApJ/743/77
- Title:
- Extremely metal-poor (XMP) galaxies in SDSS
- Short Name:
- J/ApJ/743/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carry out a systematic search for extremely metal-poor (XMP) galaxies in the spectroscopic sample of Sloan Digital Sky Survey (SDSS) data release 7 (DR7). The XMP candidates are found by classifying all the galaxies according to the form of their spectra in a region 80{AA} wide around H{alpha}. Due to the data size, the method requires an automatic classification algorithm. We use k-means. Our systematic search renders 32 galaxies having negligible [NII] lines, as expected in XMP galaxy spectra. Twenty-one of them have been previously identified as XMP galaxies in the literature - the remaining 11 are new. This was established after a thorough bibliographic search that yielded only some 130 galaxies known to have an oxygen metallicity 10 times smaller than the Sun (explicitly, with 12+log(O/H)<=7.65). XMP galaxies are rare; they represent 0.01% of the galaxies with emission lines in SDSS/DR7. Although the final metallicity estimate of all candidates remains pending, strong-line empirical calibrations indicate a metallicity about one-tenth solar, with the oxygen metallicity of the 21 known targets being 12+log(O/H)~7.61+/-0.19. Since the SDSS catalog is limited in apparent magnitude, we have been able to estimate the volume number density of XMP galaxies in the local universe, which turns out to be (1.32+/-0.23)x10^-4^Mpc^-3^. The XMP galaxies constitute 0.1% of the galaxies in the local volume, or ~0.2% considering only emission-line galaxies. All but four of our candidates are blue compact dwarf galaxies, and 24 of them have either cometary shape or are formed by chained knots.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/566/A24
- Title:
- Extremely strong damped Lyman-{alpha} systems
- Short Name:
- J/A+A/566/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of ~100 high redshift (z ~2-4) extremely strong damped Lyman-{alpha} systems (ESDLA, with N(HI)>=0.5x10^22^cm^-2^) detected in quasar spectra from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) Data Release 11. We study the neutral hydrogen, metal, and dust content of this elusive population of absorbers and confirm our previous finding that the high column density end of the N(HI) frequency distribution has a relatively shallow slope with power-law index -3.6, similar to what is seen from 21-cm maps in nearby galaxies. The stacked absorption spectrum indicates a typical metallicity ~1/20th solar, similar to the mean metallicity of the overall DLA population. The relatively small velocity extent of the low-ionisation lines suggests that ESDLAs do not arise from large-scale flows of neutral gas. The high column densities involved are in turn more similar to what is seen in DLAs associated with gamma-ray burst afterglows (GRB-DLAs), which are known to occur close to star-forming regions. This indicates that ESDLAs arise from a line of sight passing at very small impact parameters from the host galaxy, as observed in nearby galaxies. This is also supported by simple theoretical considerations and recent high-z hydrodynamical simulations. We strongly substantiate this picture by the first statistical detection of Ly{alpha} emission with <L_ESDLA_(Ly{alpha})>=~(0.6+/-0.2)x10^42^erg/s in the core of ESDLAs (corresponding to about 0.1L^*^ at z~2-3), obtained through stacking the fibre spectra (of radius 1" corresponding to ~8kpc at z~2.5). Statistical errors on the Ly{alpha} luminosity are of the order of 0.1x10^42^erg/s but we caution that the measured Ly{alpha} luminosity may be overestimated by ~35% due to sky light residuals and/or FUV emission from the quasar host and that we have neglected flux-calibration uncertainties. We estimate a more conservative uncertainty of 0.2x10^42^erg/s. The properties of the Ly{alpha} line (luminosity distribution, velocity width and velocity offset compared to systemic redshift) are very similar to that of the population of Lyman-{alpha} emitting galaxies (LAEs) with L_LAE_(Ly{alpha})>=10^41^erg/s detected in long-slit spectroscopy or narrow-band imaging surveys. By matching the incidence of ESDLAs with that of the LAEs population, we estimate the high column density gas radius to be about r_gas_=2.5kpc, i.e., significantly smaller than the radius corresponding to the BOSS fibre aperture, making fibre losses likely negligible. Finally, the average measured Ly{alpha} luminosity indicates a star-formation rate consistent with the Schmidt-Kennicutt law, SFR (M_{sun}_/yr)=~0.6/f_esc_, where f_esc_<1 is the Ly{alpha} escape fraction. Assuming the typical escape fraction of LAEs, f_esc_~0.3, the Schmidt-Kennicutt law implies a galaxy radius of about r_gal_=~2.5kpc. Finally, we note that possible overestimation of the Ly{alpha} emission would result in both smaller r_gas_ and r_gal_. Our results support a close association between LAEs and strong DLA host galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/860/83
- Title:
- 22 extreme [OIII] emitters at z~0.5 from SDSS-DR14
- Short Name:
- J/ApJ/860/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have found a sample of extreme emission-line galaxies (EELGs) with strong [OIII]{lambda}5007 emission at z~0.5. Using broadband photometric selection and requiring small uncertainties in photometry, we searched the 14th Data Release of the Sloan Digital Sky Survey (SDSS) and found 2658 candidates with strong i-band excess (i-z<=r-i-0.7). We further obtained 649 SDSS spectra of these objects, and visually identified 22 [OIII] emitters lying at 0.40<z<0.63. Having constructed their ultraviolet-infrared spectral energy distributions, we found that they have fairly blue r-W2 and red W1-W4 colors, indicative of strong, warm dust emission. Their rest-frame [OIII]{lambda}5007 equivalent widths are mostly 200-600{AA}, and their high [OIII]{lambda}5007/H{beta} ratios put them at the boundary of star-forming galaxies and active galactic nuclei on line ratio classification diagrams. The typical E(B-V) and electron temperature of [OIII] emitters are ~0.1-0.3mag and ~104K, respectively. The lowest metallicity of our [OIII] emitters with S/N[OIII]{lambda}4363>3 is 12+log(O/H)=7.98_-0.02_^+0.12^, with a median value of 8.24_-0.04_^+0.05^. Our [OIII] emitters exhibit remarkably high line luminosity-18/22 have L[OIII]{lambda}5007>5x10^42^erg/s and 5/22 have L[OIII]{lambda}5007>10^43^erg/s. Their estimated volume number density at z~0.5 is ~2x10^-8^Mpc^-3^, with L[OIII]{lambda}5007 down to ~3x10^42^erg/s. The cumulative number distribution of EELGs across different redshifts is indicative of a strong redshift evolution at the bright end of the [OIII] luminosity function.
- ID:
- ivo://CDS.VizieR/J/ApJS/222/1
- Title:
- Faint ALMA 1.2mm sources down to ~0.02mJy
- Short Name:
- J/ApJS/222/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present statistics of 133 faint 1.2mm continuum sources detected in about 120 deep Atacama Large Millimeter/submillimeter Array (ALMA) pointing data that include all the archival deep data available by 2015 June. We derive number counts of 1.2mm continuum sources down to 0.02mJy partly with the assistance of gravitational lensing, and find that the total integrated 1.2mm flux of the securely identified sources is 22.9_-5.6_^+6.7^Jy/deg2 which corresponds to 104_25_^+31^% of the extragalactic background light (EBL) measured by Cosmic Background Explorer observations. These results suggest that the major 1.2mm EBL contributors are sources with 0.02mJy, and that very faint 1.2mm sources with <~0.02mJy contribute negligibly to the EBL with the possible flattening and/or truncation of number counts in this very faint flux regime. To understand the physical origin of our faint ALMA sources, we measure the galaxy bias b_g_ by the counts-in-cells technique, and place a stringent upper limit of b_g_<3.5 that is not similar to b_g_ values of massive distant red galaxies and submillimeter galaxies but comparable to those of UV-bright, star-forming BzK galaxies (sBzKs) and Lyman break galaxies (LBGs). Moreover, in the optical and near-infrared (NIR) deep fields, we identify optical-NIR counterparts for 59% of our faint ALMA sources, the majority of which have luminosities, colors, and the IRX-{beta} relation the same as sBzKs and LBGs. We thus conclude that about a half of our faint ALMA sources are dust-poor, high-z galaxies as known as sBzKs and LBGs in optical studies, and that these faint ALMA sources are not miniature (U)LIRGs simply scaled down with the infrared brightness.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1324
- Title:
- Faint emission-line galaxies at z<=1.6
- Short Name:
- J/AJ/130/1324
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Grism Parallel Survey, a large program obtaining deep, slitless ACS grism (R~100) spectroscopy of high-latitude HST parallel fields. We identify 601 compact emission-line galaxies at z<=1.6, reaching emission lines to a flux limit of >~5x10^-18^ergs/cm^2^/s (3{sigma}). We determine redshifts by cross-correlation of the target spectra with template spectra, followed by visual inspection. We measure star formation rates from the observed [OII]{lambda}3727, [OIII]{lambda}5007, and H{alpha} line fluxes.
- ID:
- ivo://CDS.VizieR/J/AJ/124/1283
- Title:
- Faint Markarian galaxies of SBS. III.
- Short Name:
- J/AJ/124/1283
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We continue our program of spectroscopic observations of objects from the Second Byurakan Survey (SBS). This survey contains more than 3600 objects with m_pg_<19.5mag, half of them being galaxies and the other half being starlike objects. The aim of this work is to compile a complete sample of faint (B<17) Markarian galaxies. Here we present spectroscopic data for 185 galaxies, obtained with the 6m telescope of the Special Astrophysical Observatory in Russia and the 2.1m telescope of the Guillermo Haro Astrophysical Observatory in Mexico. In the present subsample, we find three new Seyfert 1 galaxies (SBS 0654+598, 1118+541, and 1320+551); one narrow-line Seyfert 1 (SBS 0748+499), one Seyfert 2 (SBS 0925+585), and three Seyfert2/LINER (SBS 0811+584, 1344+527, and 1428+529) galaxies; 12 LINERs; 13 blue compact dwarf galaxies; 65 starburst nuclei; 85 emission-line galaxies; and two absorption galaxies. Relevant astrophysical parameters (magnitude, redshift, relative intensities of emission lines, etc.) are given for the observed galaxies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/4244
- Title:
- Faint radio source population at 15.7GHz
- Short Name:
- J/MNRAS/453/4244
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A complete, flux density limited sample of 96 faint (>0.5mJy) radio sources is selected from the 10C survey at 15.7GHz in the Lockman Hole. We have matched this sample to a range of multi-wavelength catalogues, including Spitzer Extragalactic Representative Volume Survey, Spitzer Wide-area Infrared Extragalactic survey, United Kingdom Infrared Telescope Infrared Deep Sky Survey and optical data; multi-wavelength counterparts are found for 80 of the 96 sources and spectroscopic redshifts are available for 24 sources. Photometric redshifts are estimated for the sources with multi-wavelength data available; the median redshift of the sample is 0.91 with an interquartile range of 0.84. Radio-to-optical ratios show that at least 94 per cent of the sample are radio loud, indicating that the 10C sample is dominated by radio galaxies. This is in contrast to samples selected at lower frequencies, where radio-quiet AGN and star-forming galaxies are present in significant numbers at these flux density levels. All six radio-quiet sources have rising radio spectra, suggesting that they are dominated by AGN emission. These results confirm the conclusions of that the faint, flat-spectrum sources which are found to dominate the 10C sample below ~1mJy are the cores of radio galaxies. The properties of the 10C sample are compared to the Square Kilometre Array Design Studies Simulated Skies; a population of low-redshift star-forming galaxies predicted by the simulation is not found in the observed sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/795/63
- Title:
- Faraday rotation from magnesium II absorbers
- Short Name:
- J/ApJ/795/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Strong singly ionized magnesium (Mg II) absorption lines in quasar spectra typically serve as a proxy for intervening galaxies along the line of sight. Previous studies have found a correlation between the number of these Mg II absorbers and the Faraday rotation measure (RM) at ~5 GHz. We cross-match a sample of 35752 optically identified non-intrinsic Mg II absorption systems with 25649 polarized background radio sources for which we have measurements of both the spectral index and RM at 1.4 GHz. We use the spectral index to split the resulting sample of 599 sources into flat-spectrum and steep-spectrum subsamples. We find that our flat-spectrum sample shows significant (~3.5{sigma}) evidence for a correlation between Mg II absorption and RM at 1.4 GHz, while our steep-spectrum sample shows no such correlation. We argue that such an effect cannot be explained by either luminosity or other observational effects, by evolution in another confounding variable, by wavelength-dependent polarization structure in an active galactic nucleus, by the Galactic foreground, by cosmological expansion, or by partial coverage models. We conclude that our data are most consistent with intervenors directly contributing to the Faraday rotation along the line of sight, and that the intervening systems must therefore have coherent magnetic fields of substantial strength (B{bar}=1.8+/-0.4{mu}G). Nevertheless, the weak nature of the correlation will require future high-resolution and broadband radio observations in order to place it on a much firmer statistical footing.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/4
- Title:
- Far-infrared SED measurements of massive galaxies
- Short Name:
- J/ApJ/869/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive Population II galaxies undergoing the first phase of vigorous star formation after the initial Population III stage should have high energy densities and silicate-rich interstellar dust. We have modeled the resulting far-infrared spectral energy distributions (SEDs), demonstrating that they are shifted substantially to bluer ("warmer") wavelengths relative to the best fitting ones at z~3, and with strong outputs in the 10-40{mu}m range. When combined with a low level of emission by carbon dust, their SEDs match that of Haro 11, a local moderately low-metallicity galaxy undergoing a very young and vigorous starburst that is likely to approximate the relevant conditions in young Population II galaxies. We expect to see similar SEDs at high redshifts (z>~5) given the youth of galaxies at this epoch. In fact, we find a progression with redshift in observed galaxy SEDs, from those resembling local ones at 2<~z<4 to a closer resemblance with Haro 11 at 5<~z<7. In addition to the insight on conditions in high-redshift galaxies, this result implies that estimates of the total infrared luminosities at z~6 based on measurements near {lambda}~1mm can vary by factors of 2-4, depending on the SED template used. Currently popular modified blackbodies or local templates can result in significant underestimates compared with the preferred template based on the SED of Haro 11.
- ID:
- ivo://CDS.VizieR/J/ApJS/189/15
- Title:
- FeII emission in a sample of AGN spectra
- Short Name:
- J/ApJS/189/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of optical FeII emission in 302 active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey. We group the strongest FeII multiplets into three groups according to the lower term of the transition (b^4^F, a^6^S, and a^4^G terms). These approximately correspond to the blue, central, and red parts, respectively, of the "iron shelf" around H{beta}. We calculate an FeII template that takes into account transitions into these three terms and an additional group of lines, based on a reconstruction of the spectrum of I Zw 1. This FeII template gives a more precise fit of the FeII lines in broad-line AGNs than other templates. We extract FeII, H{alpha}, H{beta}, [OIII], and [NII] emission parameters and investigate correlations between them. We find that FeII lines probably originate in an intermediate line region. We note that the blue, red, and central parts of the iron shelf have different relative intensities in different objects. Their ratios depend on continuum luminosity, FWHM H{beta}, the velocity shift of FeII, and the H{alpha}/H{beta} flux ratio. We examine the dependence of the well-known anti-correlation between the equivalent widths of FeII and [OIII] on continuum luminosity. We find that there is a Baldwin effect for [OIII] but an inverse Baldwin effect for the FeII emission. The [OIII]/FeII ratio thus decreases with L_{lambda}5100_. Since the ratio is a major component of the Boroson & Green Eigenvector 1 (EV1), this implies a connection between the Baldwin effect and EV1 and could be connected with AGN evolution. We find that spectra are different for H{beta} FWHMs greater and less than ~3000km/s, and that there are different correlation coefficients between the parameters.
