- ID:
- ivo://CDS.VizieR/J/MNRAS/392/1034
- Title:
- IZJHKL' photometry of NGC 6611
- Short Name:
- J/MNRAS/392/1034
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6611 is the massive young cluster (2-3Myr) that ionizes the Eagle Nebula. We present very deep photometric observations of the central region of NGC 6611 obtained with the Hubble Space Telescope and the following filters: ACS/WFC F775W and F850LP and NIC2 F110W and F160W, loosely equivalent to ground-based IZJH filters. This survey reaches down to I~26mag. We construct the initial mass function (IMF) from ~1.5M_{sun}_ well into the brown dwarf regime (down to ~0.02M_{sun}_). We have detected 30-35 brown dwarf candidates in this sample. The low-mass IMF is combined with a higher-mass IMF constructed from the ground-based catalogue from Oliveira et al. We compare the final IMF with those of well-studied star-forming regions: we find that the IMF of NGC 6611 more closely resembles that of the low-mass star-forming region in Taurus than that of the more massive Orion Nebula Cluster. We conclude that there seems to be no severe environmental effect in the IMF due to the proximity of the massive stars in NGC 6611.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/723/251
- Title:
- Keck/LRIS confirmation of Coma membership
- Short Name:
- J/ApJ/723/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Keck/LRIS multi-object spectroscopy has been carried out on 140 of some of the lowest and highest surface brightness faint (19<R<22) dwarf galaxy candidates in the core region of the Coma Cluster. These spectra are used to measure redshifts and establish membership for these faint dwarf populations. The primary goal of the low surface brightness sample is to test our ability to use morphological and surface brightness criteria to distinguish between Coma Cluster members and background galaxies using high resolution Hubble Space Telescope/Advanced Camera for Surveys images. Candidates were rated as expected members, uncertain, or expected background. From 93 spectra, 51 dwarf galaxy members and 20 background galaxies are identified. Our morphological membership estimation success rate is ~100% for objects expected to be members and better than ~90% for galaxies expected to be in the background. We confirm that low surface brightness is a very good indicator of cluster membership. High surface brightness galaxies are almost always background with confusion arising only from the cases of the rare compact elliptical (cE) galaxies. The more problematic cases occur at intermediate surface brightness. Many of these galaxies are given uncertain membership ratings, and these were found to be members about half of the time. In a sample of 47 high surface brightness, ultracompact dwarf candidates, 19 objects have redshifts which place them in the Coma Cluster, while another 6 have questionable redshift measurements but may also prove to be members.
- ID:
- ivo://CDS.VizieR/J/AJ/153/71
- Title:
- Kepler follow-up observation program. I. Imaging
- Short Name:
- J/AJ/153/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from high-resolution, optical to near-IR imaging of host stars of Kepler Objects of Interest (KOIs), identified in the original Kepler field. Part of the data were obtained under the Kepler imaging follow-up observation program over six years (2009-2015). Almost 90% of stars that are hosts to planet candidates or confirmed planets were observed. We combine measurements of companions to KOI host stars from different bands to create a comprehensive catalog of projected separations, position angles, and magnitude differences for all detected companion stars (some of which may not be bound). Our compilation includes 2297 companions around 1903 primary stars. From high-resolution imaging, we find that ~10% (~30%) of the observed stars have at least one companion detected within 1'' (4''). The true fraction of systems with close (<~4'') companions is larger than the observed one due to the limited sensitivities of the imaging data. We derive correction factors for planet radii caused by the dilution of the transit depth: assuming that planets orbit the primary stars or the brightest companion stars, the average correction factors are 1.06 and 3.09, respectively. The true effect of transit dilution lies in between these two cases and varies with each system. Applying these factors to planet radii decreases the number of KOI planets with radii smaller than 2R_{Earth}_ by ~2%-23% and thus affects planet occurrence rates. This effect will also be important for the yield of small planets from future transit missions such as TESS.
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1163
- Title:
- Late-type galaxies in Chandra deep fields
- Short Name:
- J/ApJ/681/1163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the X-ray evolution over the last ~9Gyr of cosmic history (i.e., since z=1.4) of late-type galaxy populations in the Chandra Deep Field-North and Extended Chandra Deep Field-South (CDF-N and E-CDF-S, respectively; jointly CDFs) survey fields. Our late-type galaxy sample consists of 2568 galaxies, which were identified using rest-frame optical colors and HST morphologies. We utilized X-ray stacking analyses to investigate the X-ray emission from these galaxies, emphasizing the contributions from normal galaxies that are not dominated by active galactic nuclei (AGNs). Over this redshift range, we find significant increases (factors of ~5-10) in the X-ray-to-optical mean luminosity ratio (L_X_/L_B_) and the X-ray-to-stellar mass mean ratio (L_X_/M_*_) for galaxy populations selected by L_B_ and M_*_, respectively. When analyzing galaxy samples selected via SFR, we find that the mean X-ray-to-SFR ratio (L_X_/SFR) is consistent with being constant over the entire redshift range for galaxies with SFR=1-100M_{sun}_/yr, thus demonstrating that X-ray emission can be used as a robust indicator of star formation activity out to z~1.4. We find that the star formation activity (as traced by X-ray luminosity) per unit stellar mass in a given redshift bin increases with decreasing stellar mass over the redshift range z=0.2-1, which is consistent with previous studies of how star formation activity depends on stellar mass. Finally, we extend our X-ray analyses to Lyman break galaxies at z~3 and estimate that L_X_/L_B_ at z~3 is similar to its value at z=1.4.
- ID:
- ivo://CDS.VizieR/J/ApJ/699/1742
- Title:
- LCID project. I. Cetus and Tucana variables
- Short Name:
- J/ApJ/699/1742
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first study of the variable star populations in the isolated dwarf spheroidal galaxies (dSphs) Cetus and Tucana. Based on Hubble Space Telescope images obtained with the Advanced Camera for Surveys in the F475W and F814W bands, we identified 180 and 371 variables in Cetus and Tucana, respectively. The vast majority are RR Lyrae stars. In Cetus, we also found three anomalous Cepheids (ACs), four candidate binaries and one candidate long-period variable (LPV), while six ACs and seven LPV candidates were found in Tucana. Of the RR Lyrae stars, 147 were identified as fundamental mode (RRab) and only eight as first-overtone mode (RRc) in Cetus, with mean periods of 0.614 and 0.363 day, respectively. In Tucana, we found 216 RRab and 82 RRc giving mean periods of 0.604 and 0.353 day. These values place both galaxies in the so-called Oosterhoff Gap, as is generally the case for dSph. We found numerous RR Lyrae variables pulsating in both modes simultaneously (RRd): 17 in Cetus and 60 in Tucana. We provide the photometry and pulsation parameters for all the variables, and compare the latter with values from the literature for well studied dSph of the Local Group and Galactic globular clusters. The parallel WFPC2 fields were also searched for variables, as they lie well within the tidal radius of Cetus, and at its limit in the case of Tucana. No variables were found in the latter, while 15 were discovered in the outer field of Cetus (11 RRab, three RRc, and one RRd), even though the lower signal-to-noise ratio of the observations did not allow us to measure their periods accurately. We provide their coordinates and approximate properties for completeness.
- ID:
- ivo://CDS.VizieR/J/ApJ/712/1259
- Title:
- LCID project. II. Variables in IC1613
- Short Name:
- J/ApJ/712/1259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a new search for variable stars in the Local Group (LG) isolated dwarf galaxy IC 1613, based on 24 orbits of F475W and F814W photometry from the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. We detected 259 candidate variables in this field, of which only 13 (all of them bright Cepheids) were previously known. Out of the confirmed variables, we found 90 RR Lyrae stars, 49 classical Cepheids (including 36 new discoveries), and 38 eclipsing binary stars for which we could determine a period. The RR Lyrae include 61 fundamental (RRab) and 24 first-overtone (FO, RRc) pulsators, and five pulsating in both modes simultaneously (RRd). As for the majority of LG dwarfs, the mean periods of the RRab and RRc (0.611 and 0.334 days, respectively) as well as the fraction of overtone pulsators (f_c_=0.28) place this galaxy in the intermediate regime between the Oosterhoff types. From their position on the period-luminosity diagram and light-curve morphology, we can unambiguously classify 25 and 14 Cepheids as fundamental and FO mode pulsators, respectively. Another two are clearly second-overtone Cepheids, the first ones to be discovered beyond the Magellanic Clouds. Among the remaining candidate variables, five were classified as {delta}-Scuti and five as long-period variables. Most of the others are located on the main sequence, the majority of them likely eclipsing binary systems, although some present variations similar to pulsating stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/432/3047
- Title:
- LCID project VIII. Cepheids of Leo A
- Short Name:
- J/MNRAS/432/3047
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a new search for variable stars in the Local Group dwarf galaxy Leo A, based on deep photometry from the Advanced Camera for Surveys onboard the Hubble Space Telescope. We detected 166 bona fide variables in our field, of which about 60% are new discoveries and 33 candidate variables. Of the confirmed variables, we found 156 Cepheids, but only 10 RR Lyrae stars despite nearly 100percent completeness at the magnitude of the horizontal branch. The RR Lyrae stars include seven fundamental and three first-overtone pulsators, with mean periods of 0.636 and 0.366d, respectively. From their position on the period-luminosity (PL) diagram and light-curve morphology, we classify 91, 58 and 4 Cepheids as fundamental, first-overtone and second-overtone mode Classical Cepheids (CC), respectively, and two as Population II Cepheids. However, due to the low metallicity of Leo A, about 90percent of the detected Cepheids have periods shorter than 1.5d. Comparison with theoretical models indicate that some of the fainter stars classified as CC could be Anomalous Cepheids. We estimate the distance to Leo A using the tip of the red giant branch (TRGB) and various methods based on the photometric and pulsational properties of the Cepheids and RR Lyrae stars. The distances obtained with the TRGB and RR Lyrae stars agree well with each other while that from the Cepheid PL relations is somewhat larger, which may indicate a mild metallicity effect on the luminosity of the short-period Cepheids. Due to its very low metallicity, Leo A thus serves as a valuable calibrator of the metallicity dependences of the variable star luminosities.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/23
- Title:
- LEGUS galaxies1 observations
- Short Name:
- J/ApJS/235/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Legacy ExtraGalactic UV Survey (LEGUS) is a multiwavelength Cycle 21 Treasury program on the Hubble Space Telescope. It studied 50 nearby star-forming galaxies in 5 bands from the near-UV to the I-band, combining new Wide Field Camera 3 observations with archival Advanced Camera for Surveys data. LEGUS was designed to investigate how star formation occurs and develops on both small and large scales, and how it relates to the galactic environments. In this paper we present the photometric catalogs for all the apparently single stars identified in the 50 LEGUS galaxies. We present optical and near-UV color-magnitude diagrams for all the galaxies. For each galaxy we derived the distance from the tip of the red giant branch. We then used the NUV color-magnitude diagrams to identify stars more massive than 14M_{sun}_, and compared their number with the number of massive stars expected from the GALEX FUV luminosity. Our analysis shows that the fraction of massive stars forming in star clusters and stellar associations is about constant with the star formation rate. This lack of a relation suggests that the timescale for evaporation of unbound structures is comparable or longer than 10Myr. At low star formation rates this translates to an excess of mass in clustered environments as compared to model predictions of cluster evolution, suggesting that a significant fraction of stars form in unbound systems.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/154
- Title:
- LEGUS & Ha-LEGUS obs. of NGC4449 star clusters
- Short Name:
- J/ApJ/889/154
- Date:
- 17 Jan 2022 11:55:48
- Publisher:
- CDS
- Description:
- We present a new catalog and results for the cluster system of the starburst galaxy NGC 4449, based on multiband imaging observations taken as part of the LEGUS and H_{alpha}_-LEGUS surveys. We improve the spectral energy fitting method used to estimate cluster ages, and find that the results, particularly for older clusters, are in better agreement with those from spectroscopy. The inclusion of H{alpha} measurements, the role of stochasticity for low-mass clusters, the assumptions about reddening, and the choices of SSP model and metallicity all have important impacts on the age dating of clusters. A comparison with ages derived from stellar color-magnitude diagrams for partially resolved clusters shows reasonable agreement, but large scatter in some cases. The fraction of light found in clusters relative to the total light (i.e., T_L_) in the U, B, and V filters in 25 different ~kiloparsec-size regions throughout NGC 4449 correlates with both the specific region luminosity, R_L_, and the dominant age of the underlying stellar population in each region. The observed cluster age distribution is found to decline over time as dN/d{tau}{propto}{tau}^{gamma}^, with {gamma}=-0.85+/-0.15, independent of cluster mass, and is consistent with strong, early cluster disruption. The mass functions of the clusters can be described by a power law with dN/dM{propto}M^{beta}^ and {beta}=-1.86+/-0.2, independent of cluster age. The mass and age distributions are quite resilient to differences in age-dating methods. There is tentative evidence for a factor of 2-3 enhancement in both the star and cluster formation rate ~100-300Myr ago, indicating that cluster formation tracks star formation generally. The enhancement is probably associated with an earlier interaction event.
- ID:
- ivo://CDS.VizieR/J/MNRAS/406/1318
- Title:
- Lensed-arc statistics of galaxy clusters
- Short Name:
- J/MNRAS/406/1318
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The statistics of strongly lensed arcs in samples of galaxy clusters provide information on cluster structure that is complementary to that from individual clusters. However, samples of clusters that have been analysed to date have been either small, heterogeneous or observed with limited angular resolution. We measure the lensed-arc statistics of 97 clusters imaged at high angular resolution with the Hubble Space Telescope, identifying lensed arcs using two automated arc-detection algorithms. The sample includes similar numbers of X-ray-selected [MAssive Cluster Survey (MACS)] and optically selected [Red-Sequence Cluster Survey (RCS)] clusters, and spans cluster redshifts in the range 0.2<z<1. We compile a catalogue of 42 arcs in the X-ray-selected subsample and seven arcs in the optical subsample. All but five of these arcs are reported here for the first time.
