- ID:
- ivo://CDS.VizieR/J/A+A/507/671
- Title:
- Spectroscopy in cluster RDCS J1252.9-2927 (z=1.2)
- Short Name:
- J/A+A/507/671
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent wide-field imaging observations of the X-ray luminous cluster RDCS J1252.9-2927 at z=1.24 uncovered several galaxy groups that appear to be embedded in filamentary structure extending from the cluster core. We make a spectroscopic study of the galaxies in these groups using GMOS on Gemini-South and FORS2 on VLT with the aim of determining if these galaxies are physically associated to the cluster. We find that three groups contain galaxies at the cluster redshift and that they are probably bound to the cluster. This is the first confirmation of filamentary structure as traced by galaxy groups at z>1. We then use several spectral features in the FORS2 spectra to determine the star formation histories of group galaxies.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/132/1796
- Title:
- Spectroscopy in nearby group cores
- Short Name:
- J/AJ/132/1796
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used V and I CCD photometry to search for low surface brightness dwarf galaxies in the central (<0.5h^-1^Mpc) region of the groups NGC 6868, NGC 5846, HCG 42, and the poor cluster IC 4765. We used the exponential profile fit parameters to identify 80 low surface brightness dwarf galaxy candidates with 17mag<V<22mag (-16.7>MV>-11.4), V-I<1.5mag, {mu}_0_>22.5Vmag/arcsec^2^, h>1.5", and diameters larger than 1.2h^-1^kpc. Twenty of these galaxies are extended low surface brightness galaxies that were detected only on smoothed images, after masking all high surface brightness objects. The completeness in the sample detection is ~80% for V~<20 and 22.5Vmag/arcsec^2^<{mu}_0_<24.5Vmag/arcsec^2^. For galaxies with V>20mag and {mu}_0_>24.5Vmag/arcsec^2^, the completeness is below 50% but increases to ~80% when we search for galaxies in smoothed images.
- ID:
- ivo://CDS.VizieR/J/ApJ/834/9
- Title:
- Spectroscopy obs. of LeoA, Aqr & Sgr dwarf gal.
- Short Name:
- J/ApJ/834/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Keck/DEIMOS spectroscopy of individual stars in the relatively isolated Local Group dwarf galaxies Leo A, Aquarius, and the Sagittarius dwarf irregular galaxy. The three galaxies-but especially Leo A and Aquarius-share in common delayed star formation histories (SFHs) relative to many other isolated dwarf galaxies. The stars in all three galaxies are supported by dispersion. We found no evidence of stellar velocity structure, even for Aquarius, which has rotating HI gas. The velocity dispersions indicate that all three galaxies are dark-matter-dominated, with dark-to-baryonic mass ratios ranging from 4.4_-0.8_^+1.0^ (SagDIG) to 9.6_-1.8_^+2.5^ (Aquarius). Leo A and SagDIG have lower stellar metallicities than Aquarius, and they also have higher gas fractions, both of which would be expected if Aquarius were further along in its chemical evolution. The metallicity distribution of Leo A is inconsistent with a closed or leaky box model of chemical evolution, suggesting that the galaxy was pre-enriched or acquired external gas during star formation. The metallicities of stars increased steadily for all three galaxies, but possibly at different rates. The [{alpha}/Fe] ratios at a given [Fe/H] are lower than that of the Sculptor dwarf spheroidal galaxy, which indicates more extended SFHs than Sculptor, consistent with photometrically derived SFHs. Overall, the bulk kinematic and chemical properties for the late-forming dwarf galaxies do not diverge significantly from those of less delayed dwarf galaxies, including dwarf spheroidal galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/394/395
- Title:
- Spectroscopy of Abell 222 and Abell 223
- Short Name:
- J/A+A/394/395
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This spectroscopic study of the neighboring massive clusters Abell 222 and Abell 223 is based on MOS using EMMI at the NTT. Photometry was obtained from WFI images taken with the ESO/MPG 2.2m telescope. Data for objects coincident with objects from Proust et al., 2000A&A...355..443P, is listed for comparison.
- ID:
- ivo://CDS.VizieR/J/AJ/152/40
- Title:
- Spectroscopy of 341 bright A- and B-type stars
- Short Name:
- J/AJ/152/40
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Binary stars and higher-order multiple systems are a ubiquitous outcome of star formation, especially as the system mass increases. The companion mass-ratio distribution is a unique probe into the conditions of the collapsing cloud core and circumstellar disk(s) of the binary fragments. Inside a~1000AU the disks from the two forming stars can interact, and additionally companions can form directly through disk fragmentation. We should, therefore, expect the mass-ratio distribution of close companions (a<~100AU) to differ from that of wide companions. This prediction is difficult to test using traditional methods, in particular, with intermediate-mass primary stars, for a variety of observational reasons. We present the results of a survey searching for companions to A- and B-type stars using the direct spectral detection method, which is sensitive to late-type companions within ~1'' of the primary and which has no inner working angle. We estimate the temperatures and surface gravity of most of the 341 sample stars and derive their masses and ages. We additionally estimate the temperatures and masses of the 64 companions we find, 23 of which are new detections. We find that the mass-ratio distribution for our sample has a maximum near q~0.3. Our mass-ratio distribution has a very different form than in previous works, where it is usually well-described by a power law, and indicates that close companions to intermediate-mass stars experience significantly different accretion histories or formation mechanisms than wide companions.
- ID:
- ivo://CDS.VizieR/J/AJ/149/103
- Title:
- Spectroscopy of candidate YSOs in Serpens
- Short Name:
- J/AJ/149/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have completed an optical spectroscopic survey of a sample of candidate young stars in the Serpens Main star-forming region selected from deep B, V, and R band images. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys have been biased toward particular stages of pre-main sequence evolution. We have obtained over 700 moderate resolution optical spectra that, when combined with published data, have led to the identification of 63 association members based on the presence of H{alpha} in emission, lithium absorption, X-ray emission, a mid-infrared excess, and/or reflection nebulosity. Twelve YSOs are identified based on the presence of lithium absorption alone. An additional 16 objects are classified as possible association members and their pre-main sequence nature is in need of confirmation. Spectral types along with V and R band photometry were used to derive effective temperatures and bolometric luminosities for association members to compare with theoretical tracks and isochrones for pre-main sequence stars. An average age of 2Myr is derived for this population. When compared to simulations, there is no obvious evidence for an age spread when considering the major sources of uncertainties in the derived luminosities. However when compared to the young cluster in Ophiuchus, the association members in Serpens appear to have a larger spread in luminosities and hence ages which could be intrinsic to the region or the result of a foreground population of YSOs associated with the Aquila Rift. Modeling of the spectral energy distributions from optical through mid-infrared wavelengths has revealed three new transition disk objects, making a total of six in the cluster. Echelle spectra for a subset of these sources enabled estimates of vsini for seven association members. Analysis of gravity-sensitive lines in the echelle and moderate resolution spectra of the association members indicate surface gravities consistent with dwarf or sub-giant stars.
- ID:
- ivo://CDS.VizieR/J/AJ/126/3007
- Title:
- Spectroscopy of faint red NLTT dwarfs
- Short Name:
- J/AJ/126/3007
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present low-resolution optical spectroscopy and BVRI photometry of 453 candidate nearby stars drawn from the NLTT (<I/98>) proper-motion catalog. The stars were selected based on optical/near-infrared colors, derived by combining the NLTT photographic data with photometry from the 2MASS Second Incremental Data Release (<II/241>). Based on the derived photometric and spectroscopic parallaxes, we identify 111 stars as lying within 20pc of the Sun, including nine stars with formal distance estimates of less than 10pc. A further 53 stars have distance estimates within 1{sigma} of our 20pc limit. Almost all of those stars are additions to the nearby-star census. In total, our NLTT-based survey has so far identified 496 stars likely to be within 20pc, of which 195 are additions to nearby-star catalogs. Most of the newly identified nearby stars have spectral types between M4 and M8.
- ID:
- ivo://CDS.VizieR/J/ApJ/714/1521
- Title:
- Spectroscopy of galaxies around distant QSOs
- Short Name:
- J/ApJ/714/1521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report results from a survey of MgII absorbers in the spectra of background quasi-stellar objects (QSOs) that are within close angular distances to a foreground galaxy at z<0.5, using the Magellan Echellette Spectrograph. We have established a spectroscopic sample of 94 galaxies at a median redshift of <z>=0.24 in fields around 70 distant background QSOs (z_QSO_>0.6), 71 of which are in an "isolated" environment with no known companions and located at {rho}<~120h^-1^kpc from the line of sight of a background QSO. The rest-frame absolute B-band magnitudes span a range from M_B_-5logh=-16.4 to M_B_-5logh=-21.4 and rest-frame B_AB_-R_AB_ colors range from B_AB_-R_AB_~0 to B_AB_-R_AB_~1.5. Of these "isolated" galaxies, we find that 47 have corresponding MgII absorbers in the spectra of background QSOs and rest-frame absorption equivalent width W_r_(2796)=0.1-2.34{AA}, and 24 do not give rise to MgII absorption to sensitive upper limits.
- ID:
- ivo://CDS.VizieR/J/AJ/149/79
- Title:
- Spectroscopy of 299 galaxies from NewHa survey
- Short Name:
- J/AJ/149/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a sample of 299 H{alpha}-selected galaxies at z~~0.8, we study the relationship between galaxy stellar mass, gas-phase metallicity, and star formation rate (SFR), and compare to previous results. We use deep optical spectra obtained with the IMACS spectrograph at the Magellan telescope to measure strong oxygen lines. We combine these spectra and metallicities with (1) rest-frame UV-to-optical imaging, which allows us to determine stellar masses and dust attenuation corrections, and (2) H{alpha} narrowband imaging, which provides a robust measurement of the instantaneous SFR. Our sample spans stellar masses of ~10^9^-6x10^11^M_{sun}_, SFRs of 0.4-270M_{sun}_/yr, and metal abundances of 12+log(O/H)~~8.3-9.1(~~0.4-2.6Z_{sun}_). The correlations that we find between the H{alpha}-based SFR and stellar mass (i.e., the star-forming "main sequence") and between the stellar mass and metallicity are both consistent with previous z~1 studies of star-forming galaxies. We then study the relationship between the three properties using various plane-fitting techniques and a curve-fitting projection. In all cases, we exclude strong dependence of the M_{star}_-Z relation on SFR, but are unable to distinguish between moderate and no dependence. Our results are consistent with previous mass-metallicity-SFR studies. We check whether data set limitations may obscure a strong dependence on the SFR by using mock samples drawn from the Sloan Digital Sky Survey. These experiments reveal that the adopted signal-to-noise ratio cuts may have a significant effect on the measured dependence. Further work is needed to investigate these results, and to test whether a "fundamental metallicity relation" or a "fundamental plane" describes star-forming galaxies across cosmic time.
- ID:
- ivo://CDS.VizieR/J/AJ/154/251
- Title:
- Spectroscopy of galaxies in z=0.2-0.9 clusters
- Short Name:
- J/AJ/154/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of stellar populations in passive galaxies in seven massive X-ray clusters at z=0.19-0.89. Based on absorption-line strengths measured from our high signal-to-noise spectra, the data support primarily passive evolution of the galaxies. We use the scaling relations between velocity dispersions and the absorption-line strengths to determine representative mean line strengths for the clusters. From the age determinations based on the line strengths (and stellar population models), we find a formation redshift of z_form_=1.96_-0.19_^+0.24^. Based on line strength measurements from high signal-to-noise composite spectra of our data, we establish the relations between velocity dispersions, ages, metallicities [M/H], and abundance ratios [{alpha}/Fe] as a function of redshift. The [M/H]-velocity dispersion and [{alpha}/Fe]-velocity dispersion relations are steep and tight. The age-velocity dispersion relation is flat, with zero-point changes reflecting passive evolution. The scatter in all three parameters is within 0.08-0.15 dex at fixed velocity dispersions, indicating a large degree of synchronization in the evolution of the galaxies. We find an indication of cluster-to-cluster differences in metallicities and abundance ratios. However, variations in stellar populations with the cluster environment can only account for a very small fraction of the intrinsic scatter in the scaling relations. Thus, within these very massive clusters, the main driver of the properties of the stellar populations in passive galaxies appears to be the galaxy velocity dispersion.
