- ID:
- ivo://CDS.VizieR/J/AZh/94/648
- Title:
- Extragalactic star-forming regions
- Short Name:
- J/AZh/94/648
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relationships between atomic and molecular hydrogen and dust of various sizes in extragalactic star-forming regions are considered, based on observational data from the Spitzer and Herschel infrared space telescopes, the Very Large Array (atomic hydrogen emission) and IRAM (CO emission). The source sample consists of approximately 300 star-forming regions in 11 nearby galaxies. Aperture photometry has been applied to measure the fluxes in eight infrared bands (3.6, 4.5, 5.8, 8, 24, 70, 100, and 160um), the atomic hydrogen 21 cm line, and CO (2-1) line. The parameters of the dust in the starforming regions were determined via synthetic-spectra fitting, such as the total dust mass, the fraction of polycyclic aromatic hydrocarbons (PAHs), etc. Comparison of the observed fluxes with the measured parameters shows that the relationships between atomic hydrogen, molecular hydrogen, and dust are different in low- and high-metallicity regions. Low-metallicity regions contain more atomic gas, but less molecular gas and dust, including PAHs. The mass of dust constitutes about 1% of the mass of molecular gas in all regions considered. Fluxes produced by atomic and molecular gas do not correlate with the parameters of the stellar radiation, whereas the dust fluxes grow with increasing mean intensity of stellar radiation and the fraction of enhanced stellar radiation. The ratio of the fluxes at 8 and 24um, which characterizes the PAH content, decreases with increasing intensity of the stellar radiation, possibly indicating evolutionary variations of the PAH content. The results confirm that the contribution of the 24um emission to the total IR luminosity of extragalactic star-forming regions does not depend on the metallicity.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/801/143
- Title:
- Extrasolar Kuiper belts from Herschel
- Short Name:
- J/ApJ/801/143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study of the planet-debris disk connection can shed light on the formation and evolution of planetary systems and may help "predict" the presence of planets around stars with certain disk characteristics. In preliminary analyses of subsamples of the Herschel DEBRIS and DUNES surveys, Wyatt et al. (2012MNRAS.424.1206W) and Marshall et al. (2014A&A...565A..15M) identified a tentative correlation between debris and the presence of low-mass planets. Here we use the cleanest possible sample out of these Herschel surveys to assess the presence of such a correlation, discarding stars without known ages, with ages <1Gyr, and with binary companions <100AU to rule out possible correlations due to effects other than planet presence. In our resulting subsample of 204 FGK stars, we do not find evidence that debris disks are more common or more dusty around stars harboring high-mass or low-mass planets compared to a control sample without identified planets.
- ID:
- ivo://CDS.VizieR/J/A+A/649/L8
- Title:
- Extreme adaptive optics astrometry of R136
- Short Name:
- J/A+A/649/L8
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We compared high-contrast near-infrared images of the core of R136 taken by VLT/SPHERE, in two epochs separated by 3.06 years. For the first time we monitored the dynamics of the detected sources in the core of R136 from a ground-based telescope with adaptive optics. The aim of these observations was to search for High prOper Motion cAndidates (HOMAs) in the central region of R136 (r<6") where it has been challenging for other instruments. Two bright sources (K<15mag and V<16mag) are located near R136a1 and R136c (massive WR stars) and have been identified as potential HOMAs. These sources have significantly shifted in the images with respect to the mean shift of all reliable detected sources and their neighbours, and six times their own astrometric errors. We calculate their proper motions to be 1.36+/-0.22mas/yr^2^ (321+/-52km/s) and 1.15+/-0.11mas/yr^2^ (273+/-26km/s). We discuss different possible scenarios to explain the magnitude of such extreme proper motions, and argue for the necessity to conduct future observations to conclude on the nature of HOMAs in the core of R136.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/38
- Title:
- Extreme emission line galaxies at z<~0.05
- Short Name:
- J/ApJ/847/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Ly{alpha} emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts (z<~0.05) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at z<~0.05 (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broadband colors and studied their properties with MMT spectroscopy. From the entire SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. These blueberries are dwarf starburst galaxies with very small sizes (<1kpc) and very high ionization ([OIII]/[OII]~10-60). They also have some of the lowest stellar masses (log(M/M_{sun}_)~6.5-7.5) and lowest metallicities (7.1<12+log(O/H)<7.8) of starburst galaxies. Thus, they are small counterparts to green pea galaxies and high redshift Ly{alpha} emitting galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/742/111
- Title:
- Extreme emission-line galaxies in CANDELS
- Short Name:
- J/ApJ/742/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We identify an abundant population of extreme emission-line galaxies (EELGs) at redshift z~1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). Sixty-nine EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broadband magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission lines - with rest-frame equivalent widths ~1000{AA} - in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with ~10^8^M_{sun}_ in stellar mass, undergoing an enormous starburst phase with M_*_/(dM/dt)_*_ of only ~15Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the comoving number density (3.7x10^-4^Mpc^-3^) can produce in ~4Gyr much of the stellar mass density that is presently contained in 10^8^-10^9^M_{sun}_ dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z>1.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A1
- Title:
- Extreme Horizontal Branch stars in {omega} Cen
- Short Name:
- J/A+A/589/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in {omega} Cen. The observations performed consist of nearly 100 hours of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for aro und half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of logg, Teff and logN(He)/N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48000 and 54000K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ~2700s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary.
- ID:
- ivo://CDS.VizieR/J/MNRAS/469/347
- Title:
- Extremely Isolated Galaxies. II.
- Short Name:
- J/MNRAS/469/347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have selected a sample of 41 extremely isolated galaxies (EIGs) from the local Universe using both optical and HI Arecibo Legacy Fast ALFA survey redshifts. Narrow-band H{alpha} and wide-band imaging along with public data were used to derive star formation rates (SFRs), star formation histories and morphological classifications for the EIGs. We have found that the extreme isolation of the EIGs does not affect considerably their star formation compared to field galaxies. EIGs are typically 'blue cloud' galaxies that fit the 'main sequence of star-forming galaxies' and may show asymmetric star formation and strong compact star-forming regions. We discovered surprising environmental dependences of the HI content, M_HI_, and of the morphological type of EIGs; the most isolated galaxies (of subsample EIG-1) have lower M_HI_ on average (with 2.5{sigma} confidence) and a higher tendency to be early types (with 0.94 confidence) compared to the less isolated galaxies of subsample EIG-2. To the best of our knowledge, this is the first study that finds an effect in which an isolated sample shows a higher fraction of early types compared to a less isolated sample. Both early-type and late-type EIGs follow the same colour-to-M_*_, SFR-to-M_*_ (main sequence) and M_HI_-to-M_*_ relations. This indicates that the mechanisms and factors governing star formation, colour and the M_HI_-to-M_*_ relation are similar in early-type and late-type EIGs, and that the morphological type of EIGs is not governed by their M_HI_ content, colour or SFR.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/432/69
- Title:
- Extremely Red Objects XMM-Newton observations
- Short Name:
- J/A+A/432/69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a deep (about 80ks) XMM-Newton survey of the largest sample of near-infrared selected Extremely Red Objects (R-K>5) available to date to Ks<~19.2.
- 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.
