- ID:
- ivo://CDS.VizieR/J/ApJ/695/511
- Title:
- Young massive stars in LHA 120-N 44
- Short Name:
- J/ApJ/695/511
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent site to perform a detailed study of star formation in a mild starburst, as it hosts three regions of star formation at different evolutionary stages, and it is not as complicated and confusing as the 30 Doradus giant HII region. We have obtained Spitzer Space Telescope observations and complementary ground-based 4m uBVIJK observations of N44 to identify candidate massive young stellar objects (YSOs). We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our sample of 60 YSO candidates, ~65% of them are resolved into multiple components or extended sources in high-resolution ground-based images.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/545
- Title:
- Young stars in Cepheus OB3b
- Short Name:
- J/MNRAS/403/545
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a photometric study of I-band variability in the young association Cepheus OB3b. The study is sensitive to periodic variability on time-scales of less than a day, to more than 20d. After rejection of contaminating objects using V, I, R and narrow-band H{alpha} photometry, we find 475 objects with measured rotation periods, which are very likely pre-main-sequence members of the Cep OB3b star-forming region.
- ID:
- ivo://CDS.VizieR/J/AJ/130/188
- Title:
- Young stars in Trumpler 37 and NGC 7160
- Short Name:
- J/AJ/130/188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of MMT observations of young stars for our study of protoplanetary disks at ages 1-10Myr in two young clusters located in the Cepheus OB2 region: Trumpler 37 (embedded in the HII region IC 1396) and NGC 7160. Using low-resolution optical spectra from the Hectospec multifiber spectrograph, we have tripled the number of known low-mass cluster members, identifying 130 new members in Tr 37 and 30 in NGC 7160. We use indicators of youth (Li absorption at 6707{AA}) and accretion/chromospheric activity (H{alpha} emission) to identify and classify the low-mass cluster members. We derive spectral types for all the low-mass candidates and calculate the individual extinctions and the average over the clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/856/80
- Title:
- 6-yr optical monitoring of the FSRQ 3C 454.3
- Short Name:
- J/ApJ/856/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our photometric monitoring of a flat spectrum radio quasar 3C 454.3 at Yunnan observatories from 2006 to 2011. We find that the optical color of 3C 454.3 shows an obvious redder-when-brighter trend, which reaches a saturation stage when the source is brighter than 15.15mag at V band. We perform a simulation with multiple values of disk luminosity and spectral index to reproduce the magnitude-color diagram. The results show that the contamination caused by the disk radiation alone is difficult to produce the observed color variability. The variability properties during the outburst in 2009 December are also compared with {gamma}-ray data derived from the Fermi {gamma}-ray space telescope. The flux variation of these two bands follows a linear relation with F_{gamma}_{propto}F_R_^1.14+/-0.07^, which provides observational evidence for the external Compton process in 3C 454.3. Meanwhile, this flux correlation indicates that electron injection is the main mechanism for the variability origin. We also explore the variation of the flux ratio F{gamma}/FR and the detailed structures in the light curves, and discuss some possible origins for the detailed variability behaviors.
- ID:
- ivo://CDS.VizieR/J/ApJ/785/162
- Title:
- YSO candidates in the Magellanic Bridge
- Short Name:
- J/ApJ/785/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are ~10 M_{sun}_<<45 M_{sun}_ found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given H I column density, N(H I). We found that the LMC has ~3xhigher probability than the Bridge for N(H I)>12x10^20^/cm^2^, but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to H I is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.
- ID:
- ivo://CDS.VizieR/J/A+A/542/A66
- Title:
- YSOs in 9 LMC star forming regions
- Short Name:
- J/A+A/542/A66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We introduce a new set of selection criteria for the identification of infrared bright young stellar object (YSO) candidates and apply them to nine HII regions in the Large Magellanic Cloud (LMC), focusing particularly on lower mass candidates missed by most surveys. Data are from the Spitzer Space Telescope legacy program SAGE (Surveying the Agents of Galaxy Evolution; Meixner et al. 2006, Cat. J/AJ/132/2268, see also II/305), combined with optical photometry from the Magellanic Clouds Photometric Survey (MCPS; Zaritsky et al. 1997AJ....114.1002Z) and near-infrared photometry from the InfraRed Survey Facility (IRSF; Kato et al. 2007, Cat. II/288). We choose regions of diverse physical size, star formation rates (SFRs), and ages. We also cover a wide range of locations and surrounding environments in the LMC. These active star-forming regions are LHA 120-N 11, N 44, N 51, N 105, N 113, N 120, N 144, N 160, and N 206. Some have been well-studied (e.g., N11, N44, N160) in the past, while others (e.g., N51, N144) have received little attention. We identify 1045 YSO candidates, including 918 never before identified and 127 matching previous candidate lists. We characterize the evolutionary stage and physical properties of each candidate using the spectral energy distribution (SED) fitter of Robitaille et al. (2007ApJS..169..328R) and estimate mass functions and SFRs for each region.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/79
- Title:
- YSOs search in LDN 1340 in optical
- Short Name:
- J/ApJ/822/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed an optical spectroscopic and photometric search for young stellar objects associated with the molecular cloud Lynds 1340, and examined the structure of the cloud by constructing an extinction map, based on SDSS data. The new extinction map suggests a shallow, strongly fragmented cloud, having a mass of some 3700M_{sun}_. Longslit spectroscopic observations of the brightest stars over the area of L1340 revealed that the most massive star associated with L1340 is a B4-type, ~5M_{sun}_ star. The new spectroscopic and photometric data of the intermediate-mass members led to a revised distance of 825_-80_^+110^pc, and revealed seven members of the young stellar population with M>~2M_{sun}_. Our search for H{alpha} emission line stars, conducted with the Wide Field Grism Spectrograph 2 on the 2.2m telescope of the University of Hawaii and covering a 30'x40' area, resulted in the detection of 75 candidate low-mass pre-main sequence stars, 58 of which are new. We constructed spectral energy distributions (SEDs) of our target stars, based on SDSS, 2MASS, Spitzer, and WISE photometric data, derived their spectral types, extinctions, and luminosities from BVRIJ fluxes, estimated masses by means of pre-main sequence evolutionary models, and examined the disk properties utilizing the 2-24{mu}m interval of the SED. We measured the equivalent width of the H{alpha} lines and derived accretion rates. The optically selected sample of pre-main sequence stars has a median effective temperature of 3970K, a stellar mass of 0.7M_{sun}_, and an accretion rate of 7.6x10^-9^M_{sun}_/yr.
- ID:
- ivo://CDS.VizieR/J/MNRAS/448/3167
- Title:
- z>~5 AGN in Chandra Deep Field-South
- Short Name:
- J/MNRAS/448/3167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate early black hole (BH) growth through the methodical search for z>~5 active galactic nuclei (AGN) in the Chandra} Deep Field South. We base our search on the Chandra 4-Ms data with flux limits of 9.1x10^-18^erg/s/cm2 (soft, 0.5-2keV) and 5.5x10^-17^erg/s/cm2 (hard, 2-8keV). At z~5, this corresponds to luminosities as low as ~10^42^erg/s/cm2 (~10^43^erg/s) in the soft (hard) band and should allow us to detect Compton-thin AGN with M_BH_>10^7^M_{sun}_ and Eddington ratios >0.1. Our field (0.03deg^2^) contains over 600 z~5 Lyman Break Galaxies. Based on lower redshift relations, we would expect ~20 of them to host AGN. After combining the Chandra data with Great Observatories Origins Deep Survey (GOODS)/Advanced Camera for Surveys (ACS), CANDELS/Wide Field Camera 3 and Spitzer/Infrared Array Camera data, the sample consists of 58 high-redshift candidates. We run a photometric redshift code, stack the GOODS/ACS data, apply colour criteria and the Lyman Break Technique and use the X-ray Hardness Ratio. We combine our tests and using additional data find that all sources are most likely at low redshift. We also find five X-ray sources without a counterpart in the optical or infrared which might be spurious detections. We conclude that our field does not contain any convincing z>~5 AGN. Explanations for this result include a low BH occupation fraction, a low AGN fraction, short, super-Eddington growth modes, BH growth through BH-BH mergers or in optically faint galaxies. By searching for z>~5 AGN, we are setting the foundation for constraining early BH growth and seed formation scenarios.
- ID:
- ivo://CDS.VizieR/J/ApJ/826/114
- Title:
- z~3-6 protoclusters in the CFHTLS deep fields
- Short Name:
- J/ApJ/826/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the discovery of three protoclusters at z~3-4 with spectroscopic confirmation in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. In these fields, we investigate the large-scale projected sky distribution of z~3-6 Lyman-break galaxies and identify 21 protocluster candidates from regions that are overdense at more than 4{sigma} overdensity significance. Based on cosmological simulations, it is expected that more than 76% of these candidates will evolve into a galaxy cluster of at least a halo mass of 10^14^ M_{sun}_ at z=0. We perform follow-up spectroscopy for eight of the candidates using Subaru/FOCAS, Keck II/DEIMOS, and Gemini-N/GMOS. In total we target 462 dropout candidates and obtain 138 spectroscopic redshifts. We confirm three real protoclusters at z=3-4 with more than five members spectroscopically identified and find one to be an incidental overdense region by mere chance alignment. The other four candidate regions at z~5-6 require more spectroscopic follow-up in order to be conclusive. A z=3.67 protocluster, which has 11 spectroscopically confirmed members, shows a remarkable core-like structure composed of a central small region (<0.5 physical Mpc) and an outskirts region (~1.0 physical Mpc). The Ly{alpha} equivalent widths of members of the protocluster are significantly smaller than those of field galaxies at the same redshift, while there is no difference in the UV luminosity distributions. These results imply that some environmental effects start operating as early as at z~4 along with the growth of the protocluster structure. This study provides an important benchmark for our analysis of protoclusters in the upcoming Subaru/HSC imaging survey and its spectroscopic follow-up with the Subaru/PFS that will detect thousands of protoclusters up to z~6.
- ID:
- ivo://CDS.VizieR/J/ApJ/895/32
- Title:
- Zwicky Transient Facility BTS. I.
- Short Name:
- J/ApJ/895/32
- Date:
- 16 Mar 2022 00:25:08
- Publisher:
- CDS
- Description:
- The Zwicky Transient Facility (ZTF) is performing a three-day cadence survey of the visible northern sky (~3{pi}) with newly found transient candidates announced via public alerts. The ZTF Bright Transient Survey (BTS) is a large spectroscopic campaign to complement the photometric survey. BTS endeavors to spectroscopically classify all extragalactic transients with m_peak_<~18.5mag in either the g_ZTF_ or r_ZTF_ filters, and publicly announce said classifications. BTS discoveries are predominantly supernovae (SNe), making this the largest flux-limited SN survey to date. Here we present a catalog of 761 SNe, classified during the first nine months of ZTF (2018 April 1-2018 December 31). We report BTS SN redshifts from SN template matching and spectroscopic host-galaxy redshifts when available. We analyze the redshift completeness of local galaxy catalogs, the redshift completeness fraction (RCF; the ratio of SN host galaxies with known spectroscopic redshift prior to SN discovery to the total number of SN hosts). Of the 512 host galaxies with SNe Ia, 227 had previously known spectroscopic redshifts, yielding an RCF estimate of 44%{+/-}4%. The RCF decreases with increasing distance and decreasing galaxy luminosity (for z<0.05, or ~200Mpc, RCF~0.6). Prospects for dramatically increasing the RCF are limited to new multifiber spectroscopic instruments or wide-field narrowband surveys. Existing galaxy redshift catalogs are only ~50% complete at r~16.9mag. Pushing this limit several magnitudes deeper will pay huge dividends when searching for electromagnetic counterparts to gravitational wave events or sources of ultra-high-energy cosmic rays or neutrinos.