- ID:
- ivo://CDS.VizieR/J/AJ/148/122
- Title:
- YSOVAR: infrared photometry in Lynds 1688
- Short Name:
- J/AJ/148/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The emission from young stellar objects (YSOs) in the mid-infrared (mid-IR) is dominated by the inner rim of their circumstellar disks. We present IR data from the Young Stellar Object VARiability (YSOVAR) survey of ~800 objects in the direction of the Lynds 1688 (L1688) star-forming region over four visibility windows spanning 1.6yr using the Spitzer Space Telescope in its warm mission phase. Among all light curves, 57 sources are cluster members identified based on their spectral energy distribution and X-ray emission. Almost all cluster members show significant variability. The amplitude of the variability is larger in more embedded YSOs. Ten out of 57 cluster members have periodic variations in the light curves with periods typically between three and seven days, but even for those sources, significant variability in addition to the periodic signal can be seen. No period is stable over 1.6yr. Nonperiodic light curves often still show a preferred timescale of variability that is longer for more embedded sources. About half of all sources exhibit redder colors in a fainter state. This is compatible with time-variable absorption toward the YSO. The other half becomes bluer when fainter. These colors can only be explained with significant changes in the structure of the inner disk. No relation between mid-IR variability and stellar effective temperature or X-ray spectrum is found.
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- ID:
- ivo://CDS.VizieR/J/AJ/150/175
- Title:
- YSOVAR: infrared photometry in NGC 1333
- Short Name:
- J/AJ/150/175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of the Young Stellar Object VARiability (YSOVAR) program, we monitored NGC 1333 for ~35 days at 3.6 and 4.5{mu}m using the Spitzer Space Telescope. We report here on the mid-infrared variability of the point sources in the ~10'x~20' area centered on 03:29:06, +31:19:30 (J2000). Out of 701 light curves in either channel, we find 78 variables over the YSOVAR campaign. About half of the members are variable. The variable fraction for the most embedded spectral energy distributions (SEDs) (Class I, flat) is higher than that for less embedded SEDs (Class II), which is in turn higher than the star-like SEDs (Class III). A few objects have amplitudes (10-90th percentile brightness) in [3.6] or [4.5]>0.2mag; a more typical amplitude is 0.1-0.15mag. The largest color change is >0.2mag. There are 24 periodic objects, with 40% of them being flat SED class. This may mean that the periodic signal is primarily from the disk, not the photosphere, in those cases. We find 9 variables likely to be "dippers", where texture in the disk occults the central star, and 11 likely to be "bursters", where accretion instabilities create brightness bursts. There are 39 objects that have significant trends in [3.6]-[4.5] color over the campaign, about evenly divided between redder-when-fainter (consistent with extinction variations) and bluer-when-fainter. About a third of the 17 Class 0 and/or jet-driving sources from the literature are variable over the YSOVAR campaign, and a larger fraction (~half) are variable between the YSOVAR campaign and the cryogenic-era Spitzer observations (6-7 years), perhaps because it takes time for the envelope to respond to changes in the central source. The NGC 1333 brown dwarfs do not stand out from the stellar light curves in any way except there is a much larger fraction of periodic objects (~60% of variable brown dwarfs are periodic, compared to ~30% of the variables overall).
- ID:
- ivo://CDS.VizieR/J/ApJ/753/149
- Title:
- YSOVAR: six eclipsing binaries in Orion
- Short Name:
- J/ApJ/753/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for ~2400 candidate Orion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass ({theta}^1^ Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797M_{sun}_) and longest-period (ISOY J053505.71-052354.1, P~20 days) PMS EBs currently known. In two cases ({theta}^1^ Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.
- 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/813/78
- Title:
- z=4.5 and z=5.7 LAEs properties with Spitzer
- Short Name:
- J/ApJ/813/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a stellar population modeling analysis of a sample of 162 z=4.5 and 14 z=5.7 Ly{alpha} emitting galaxies (LAEs) in the Bootes field, using deep Spitzer/IRAC data at 3.6 and 4.5 {mu}m from the Spitzer Ly{alpha} Survey, along with Hubble Space Telescope NICMOS and WFC3 imaging at 1.1 and 1.6 {mu}m for a subset of the LAEs. This represents one of the largest samples of high-redshift LAEs imaged with Spitzer IRAC. We find that 30/162 (19%) of the z=4.5 LAEs and 9/14 (64%) of the z=5.7 LAEs are detected at >=3{sigma} in at least one IRAC band. Individual z=4.5 IRAC-detected LAEs have a large range of stellar mass, from 5x10^8^-10^11^ M_{sun}_. One-third of the IRAC-detected LAEs have older stellar population ages of 100 Myr^-1^ Gyr, while the remainder have ages <100 Myr. A stacking analysis of IRAC-undetected LAEs shows this population to be primarily low mass (8-20x10^8^ M_{sun}_) and young (64-570 Myr). We find a correlation between stellar mass and the dust-corrected ultraviolet-based star formation rate (SFR) similar to that at lower redshifts, in that higher mass galaxies exhibit higher SFRs. However, the z=4.5 LAE correlation is elevated 4-5 times in SFR compared to continuum-selected galaxies at similar redshifts. The exception is the most massive LAEs which have SFRs similar to galaxies at lower redshifts suggesting that they may represent a different population of galaxies than the traditional lower-mass LAEs, perhaps with a different mechanism promoting Ly{alpha} photon escape.
- ID:
- ivo://CDS.VizieR/J/ApJ/684/905
- Title:
- z>1 galaxy clusters from IRAC Shallow Survey
- Short Name:
- J/ApJ/684/905
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified 335 galaxy cluster and group candidates, 106 of which are at z>1, using a 4.5um-selected sample of objects from a 7.25deg^2^ region in the Spitzer Infrared Array Camera (IRAC) Shallow Survey. Clusters were identified as three-dimensional overdensities using a wavelet algorithm, based on photometric redshift probability distributions derived from IRAC and NOAO Deep Wide-Field Survey data. We estimate only ~10% of the detections are spurious. To date 12 of the z>1 candidates have been confirmed spectroscopically, at redshifts from 1.06 to 1.41. Velocity dispersions of ~750km/s for two of these argue for total cluster masses well above 10^14^M_{sun}_, as does the mass estimated from the rest-frame near-infrared stellar luminosity. Although not selected to contain a red sequence, some evidence for red sequences is present in the spectroscopically confirmed clusters, and brighter galaxies are systematically redder than the mean galaxy color in clusters at all redshifts.
- ID:
- ivo://CDS.VizieR/J/PASJ/65/113
- Title:
- 0.006<=z<=0.8 IR galaxies with AKARI
- Short Name:
- J/PASJ/65/113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the 9 and 18um luminosity functions (LFs) of galaxies at 0.006<=z<=0.8 (with an average redshift of ~0.04) using the AKARI mid-infrared all-sky survey catalog. We selected 243 galaxies at 9um and 255 galaxies at 18um from the Sloan Digital Sky Survey (SDSS) spectroscopy region. These galaxies were then classified by their optical emission lines, such as the line width of H{alpha} or by their emission line ratios of [OIII]/H{beta} and [NII]/H{alpha} into five types: Type 1 active galactic nuclei (AGN) (Type 1); Type 2 AGN (Type 2); low-ionization narrow emission line galaxies (LINER); galaxies with both star formation and narrow-line AGN activity (composite galaxies); and star-forming galaxies (SF). We found that (i) the number density ratio of Type 2 to Type 1 AGNs is 1.73+/-0.36, which is larger than a result obtained from the optical LF and (ii) this ratio decreases with increasing 18um luminosity.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A73
- Title:
- ZJ VISTA photometry in NGC253 stellar halo
- Short Name:
- J/A+A/562/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use images obtained with the VISTA telescope in the Z and J bands to analyze the stellar content of NGC 253, a nearly edge on spiral galaxy in the Sculptor group. The very deep photometry, down to J~23.5, and the wide area covered allow us to trace the red giant branch and asymptotic giant branch (AGB) stars that belong to the outer disk and the halo of NGC 253, out to 50kpc along the galaxy minor axis. We confirm the existence of an extraplanar component, with a prominent southern shelf and detect for the first time a symmetrical feature on the north side. The star counts profile along the major axis show a clear break at 25kpc from the center, signalling the transition from the disk to the halo. The isodensity contours show a flat inner halo that blends with a more extended, diffuse, rounder outer halo. In such external structure, we detect an overdensity at about 28kpc from the plane and extending over 20kpc parallel with the disk of the galaxy. The spatially resolved color magnitude diagrams show a rather homogeneous stellar population across the tile. Particularly surprising is the presence of bright, intermediate age, AGB stars found scattered over a large volume.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/158
- Title:
- z<0.5 PG quasars IR energy distributions
- Short Name:
- J/ApJ/854/158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interstellar medium is crucial to understanding the physics of active galaxies and the coevolution between supermassive black holes and their host galaxies. However, direct gas measurements are limited by sensitivity and other uncertainties. Dust provides an efficient indirect probe of the total gas. We apply this technique to a large sample of quasars, whose total gas content would be prohibitively expensive to measure. We present a comprehensive study of the full (1 to 500{mu}m) infrared spectral energy distributions of 87 redshift <0.5 quasars selected from the Palomar-Green sample, using photometric measurements from 2MASS, WISE, and Herschel, combined with Spitzer mid-infrared (5-40{mu}m) spectra. With a newly developed Bayesian Markov Chain Monte Carlo fitting method, we decompose various overlapping contributions to the integrated spectral energy distribution, including starlight, warm dust from the torus, and cooler dust on galaxy scales. This procedure yields a robust dust mass, which we use to infer the gas mass, using a gas-to-dust ratio constrained by the host galaxy stellar mass. Most (90%) quasar hosts have gas fractions similar to those of massive, star-forming galaxies, although a minority (10%) seem genuinely gas-deficient, resembling present-day massive early-type galaxies. This result indicates that "quasar mode" feedback does not occur or is ineffective in the host galaxies of low-redshift quasars. We also find that quasars can boost the interstellar radiation field and heat dust on galactic scales. This cautions against the common practice of using the far-infrared luminosity to estimate the host galaxy star formation rate.
- 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.