- ID:
- ivo://CDS.VizieR/J/ApJ/863/92
- Title:
- LAE cand. at z~5.7 in the field of QSO J0148+0600
- Short Name:
- J/ApJ/863/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The observed scatter in intergalactic Ly{alpha} opacity at z<~6 requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. Post-reionization models that explain this scatter invoke fluctuations in either the ionizing ultraviolet background (UVB) or IGM temperature. These models make very different predictions, however, for the relationship between Ly{alpha} opacity and local density. Here, we test these models using Ly{alpha}-emitting galaxies (LAEs) to trace the density field surrounding the longest and most opaque known Ly{alpha} trough at z<6. Using deep Subaru Hyper Suprime-Cam narrowband imaging, we find a highly significant deficit of z~5.7 LAEs within 20h^-1^Mpc of the trough. The results are consistent with a model in which the scatter in Ly{alpha} opacity near z~6 is driven by large-scale UVB fluctuations, and disfavor a scenario in which the scatter is primarily driven by variations in IGM temperature. UVB fluctuations at this epoch present a boundary condition for reionization models, and may help shed light on the nature of the ionizing sources.
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- ID:
- ivo://CDS.VizieR/J/ApJ/744/110
- Title:
- LAE galaxies between 2.1=<z<=3.1
- Short Name:
- J/ApJ/744/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe the results of a new, wide-field survey for z=3.1 Ly{alpha} emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S). By using a nearly top-hat 5010{AA} filter and complementary broadband photometry from the MUSYC survey, we identify a complete sample of 141 objects with monochromatic fluxes brighter than 2.4x10^-17^erg/cm^2^/s and observers-frame equivalent widths (EWs) greater than ~80{AA} (i.e., 20{AA} in the rest frame of Ly{alpha}). The bright end of this data set is dominated by X-ray sources and foreground objects with Galaxy Evolution Explorer detections, but when these interlopers are removed, we are still left with a sample of 130 LAE candidates, 39 of which have spectroscopic confirmations. This sample overlaps the set of objects found in an earlier ECDF-S survey, but due to our filter's redder bandpass, it also includes 68 previously uncataloged sources. We confirm earlier measurements of the z=3.1 LAE emission-line luminosity function and show that an apparent anticorrelation between EW and continuum brightness is likely due to the effect of correlated errors in our heteroskedastic data set. Finally, we compare the properties of z=3.1 LAEs to LAEs found at z=2.1. We show that in the ~1Gyr after z~3, the LAE luminosity function evolved significantly, with L* fading by ~0.4mag, the number density of sources with L>1.5x10^42^erg/s declining by ~50%, and the EW scale length contracting from 70^+7^_-5_{AA} to 50^+9^_-6_{AA}. When combined with literature results, our observations demonstrate that over the redshift range z~0 to z~4, LAEs contain less than ~10% of the star formation rate density of the universe.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/95
- Title:
- LAE galaxies in the ECDF-S at z~2.1 and z~3.1
- Short Name:
- J/ApJ/753/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a rest-frame ultraviolet morphological analysis of 108 z~2.1 Ly{alpha} emitters (LAEs) in the Extended Chandra Deep Field South and compare it to a similar sample of 171 LAEs at z~3.1. Using Hubble Space Telescope images from the Galaxy Evolution from Morphology and SEDs survey, Great Observatories Origins Deep Survey, and Hubble Ultradeep Field, we measure size and photometric component distributions, where photometric components are defined as distinct clumps of UV-continuum emission. At both redshifts, >80% of LAEs have observed half-light radii <2kpc, but the median half-light radius rises from 0.95+/-0.04kpc at z=3.1 to 1.41+/-0.14kpc at z=2.1. A similar evolution is seen in the sizes of individual rest-UV components, but there is no evidence for evolution in the number of multi-component systems. In the z=2.1 sample, we see clear correlations between the size of an LAE and other physical properties derived from its spectral energy distribution (SED). LAEs are found to be larger for galaxies with higher stellar mass, star formation rate, and dust obscuration, but there is no evidence for a trend between equivalent width and half-light radius at either redshift. The presence of these correlations suggests that a wide range of objects are being selected by LAE surveys at z~2, including a significant fraction of objects for which a massive and moderately extended population of old stars underlies the young starburst giving rise to the Ly{alpha} emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/865/L1
- Title:
- LAEs discovered with ultra-deep MUSE sp. in UDF
- Short Name:
- J/ApJ/865/L1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using an ultra-deep blind survey with the MUSE integral field spectrograph on the European Southern Observatory Very Large Telescope, we obtain spectroscopic redshifts to a depth never before explored: galaxies with observed magnitudes m_AB_>~30-32. Specifically, we detect objects via Ly{alpha} emission at 2.9<z<6.7 without individual continuum counterparts in areas covered by the deepest optical/near-infrared imaging taken by the Hubble Space Telescope, the Hubble Ultra Deep Field. In total, we find 102 such objects in 9 square arcminutes at these redshifts. Detailed stacking analyses confirm the Ly{alpha} emission as well as the 1216 {AA} breaks and faint ultraviolet continua (M_UV_~-15). This makes them the faintest spectroscopically confirmed objects at these redshifts, similar to the sources believed to reionize the universe. A simple model for the expected fraction of detected/undetected Ly{alpha} emitters as a function of luminosity is consistent with these objects being the high-equivalent width tail of the normal Ly{alpha}-emitter population at these redshifts.
- ID:
- ivo://CDS.VizieR/J/ApJ/622/129
- Title:
- Lag-luminosity relationship in AGN
- Short Name:
- J/ApJ/622/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We determine interband lags between variations in the B band and variations in the V, R, and I bands for 14 active galactic nuclei observed at the Crimean Astrophysical Observatory. The computed lags range from tenths of a day to several days, and it is positive (that is, V, R, and I bands lag behind the B band) in most cases, except for a few cases for the V filter.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/1026
- Title:
- Lagoon Nebula M8 T tauri accretion rates
- Short Name:
- J/MNRAS/453/1026
- Date:
- 03 Nov 2021
- Publisher:
- CDS
- Description:
- We estimate the accretion rates of 235 Classical T Tauri star (CTTS) candidates in the Lagoon Nebula using ugri H{alpha} photometry from the VST Photometric H{alpha} survey+. Our sample consists of stars displaying H{alpha} excess, the intensity of which is used to derive accretion rates. For a subset of 87 stars, the intensity of the u-band excess is also used to estimate accretion rates. We find the mean variation in accretion rates measured using H{alpha} and u-band intensities to be ~0.17dex, agreeing with previous estimates (0.04-0.4dex) but for a much larger sample. The spatial distribution of CTTS align with the location of protostars and molecular gas suggesting that they retain an imprint of the natal gas fragmentation process. Strong accretors are concentrated spatially, while weak accretors are more distributed. Our results do not support the sequential star-forming processes suggested in the literature.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/51
- Title:
- Lagoon Nebula stars. I. Rotation periods
- Short Name:
- J/ApJ/747/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a long-term, wide-field, high-cadence photometric monitoring survey of ~50000 stars in the Lagoon Nebula H II region. This first paper presents rotation periods for 290 low-mass stars in NGC 6530, the young cluster illuminating the nebula, and for which we assemble a catalog of infrared and spectroscopic disk indicators, estimated masses and ages, and X-ray luminosities. The distribution of rotation periods we measure is broadly uniform for 0.5days<P<10days; the short-period cutoff corresponds to breakup. We observe no obvious bimodality in the period distribution, but we do find that stars with disk signatures rotate more slowly on average. The stars' X-ray luminosities are roughly flat with rotation period, at the saturation level (log L_X_/L_bol_{approx} -3.3). However, we find a significant positive correlation between L_X_/L_bol_ and corotation radius, suggesting that the observed X-ray luminosities are regulated by centrifugal stripping of the stellar coronae. The period-mass relationship in NGC 6530 is broadly similar to that of the Orion Nebula Cluster (ONC), but the slope of the relationship among the slowest rotators differs from that in the ONC and other young clusters. We show that the slope of the period-mass relationship for the slowest rotators can be used as a proxy for the age of a young cluster, and we argue that NGC 6530 may be slightly younger than the ONC, making it a particularly important touchstone for models of angular momentum evolution in young, low-mass stars.
- ID:
- ivo://CDS.VizieR/J/AJ/121/2124
- Title:
- {lambda} Ori pre-main-sequence stars photometry
- Short Name:
- J/AJ/121/2124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The {lambda} Ori star-forming region presents a snapshot of a moderate-mass giant molecular cloud 1-2Myr after cloud disruption by OB stars, with the OB stars, the low-mass stellar population, remnant molecular clouds, and the dispersed gas all still present. We have used optical photometry and multiobject spectroscopy for lithium absorption to identify 266 pre-main-sequence stars in 8deg^2^ of the region. We also present new Stroemgren photometry for the massive stars, from which we derive a distance of 450pc and a turnoff age of 6-7Myr. Using these parameters and pre-main-sequence evolutionary models, we map the star formation history of the low-mass stars. We find that low-mass star formation started throughout the region at about the same time as the birth of the massive stars, and thereafter the birth rate accelerated. Within the last 1-2Myr star formation ceased in the center of the star-forming region, near the concentration of OB stars, while it continues in dark clouds 20pc away. We suggest that a supernova 1-2Myr ago destroyed the molecular cloud core from which the OB stars formed, but it did not terminate star formation in more distant reaches of the giant molecular cloud. We find no secure evidence for triggered or sequential star formation in the outer molecular clouds. The global star formation of the {lambda} Ori region has generated the field initial mass function, but local star formation in subregions shows large deviations from the expected ratio of high- to low-mass stars.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A34
- Title:
- LAMOST DR4 New mercury-manganese stars
- Short Name:
- J/A+A/645/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The present work presents our efforts at identifying new mercury-manganese (HgMn/CP3) stars using spectra obtained with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Suitable candidates were searched for among pre-selected early-type spectra from LAMOST DR4 using a modified version of the MKCLASS code that probes several HgII and MnII features. The spectra of the resulting 332 candidates were visually inspected. Using parallax data and photometry from Gaia DR2, we investigated magnitudes, distances from the Sun, and the evolutionary status of our sample stars. We also searched for variable stars using diverse photometric survey sources. We present 99 bona fide CP3 stars, 19 good CP3 star candidates, and seven candidates. Our sample consists of mostly new discoveries and contains, on average, the faintest CP3 stars known (peak distribution 9.5<=G<=13.5mag). All stars are contained within the narrow spectral temperature-type range from B6 to B9.5, in excellent agreement with the expectations and the derived mass estimates (2.4<=M_{sun}_<=4 for most objects). Our sample stars are between 100Myr and 500Myr old and cover the whole age range from zero-age to terminal-age main sequence. They are almost homogeneously distributed at fractional ages on the main sequence <=80%, with an apparent accumulation of objects between fractional ages of 50% to 80%. We find a significant impact of binarity on the mass and age estimates. Eight photometric variables were discovered, most of which show monoperiodic variability in agreement with rotational modulation. Together with the recently published catalogue of APOGEE CP3 stars, our work significantly increases the sample size of known Galactic CP3 stars, paving the way for future in-depth statistical studies.
- ID:
- ivo://CDS.VizieR/J/ApJS/238/16
- Title:
- LAMOST-DR3 very metal-poor star catalog
- Short Name:
- J/ApJS/238/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the result of a search for very metal-poor (VMP, [Fe/H]{<}-2.0) stars in the Milky Way based on low-resolution spectra from Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) DR3, significantly enlarging the current candidate sample of these low-metallicity objects. The selection procedure results in a sample of 10008 VMP stars covering a large area of sky in the Northern Hemisphere, and includes over 6800 targets brighter than V~16. This LAMOST DR3 VMP sample provides the largest number of VMP candidates to date that are sufficiently bright for follow-up high-resolution observation with 4-10m telescopes, greatly expanding the VMP stars discovered in the northern sky, and can be used to balance the spatial distribution of VMP stars with high-resolution spectroscopic analyses. Comparison with stars having existing high-resolution analyses and Tycho Gaia Astrometric Solution parallaxes indicates that the derived stellar parameters and distance estimates are reliable. The sample reaches beyond 40kpc in the halo, and contains over 670 candidates of extremely metal-poor ([Fe/H]{<}-3.0) and ultra-metal-poor ([Fe/H]{<}-4.0) stars. The distribution of V{phi} indicates that the sample consists of two halo components, with the retrograde component likely to be associated with the outer-halo population. A new criterion is proposed to select carbon-enhanced metal-poor (CEMP) star candidates, using line indices G1 and EGP over the range 4000K<Teff<7000K, resulting in 636 CEMP candidates from the LAMOST DR3 VMP sample.
