- ID:
- ivo://CDS.VizieR/J/ApJ/826/32
- Title:
- HST observations of star clusters in NGC 3256
- Short Name:
- J/ApJ/826/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Advanced Camera for Surveys on the Hubble Space Telescope to study the rich population of young massive star clusters in the main body of NGC 3256, a merging pair of galaxies with a high star formation rate (SFR) and SFR per unit area ({Sigma}_SFR_). These clusters have luminosity and mass functions that follow power laws, dN/dL{propto}L^{alpha}^ with {alpha}=-2.23+/-0.07, and dN/dM{propto}M^{beta}^ with {beta}=-1.86+/-0.34 for {tau}<10Myr clusters, similar to those found in more quiescent galaxies. The age distribution can be described by dN/d{tau}{propto}{tau}^{gamma}^, with {gamma}~-0.67+/-0.08 for clusters younger than about a few hundred million years, with no obvious dependence on cluster mass. This is consistent with a picture where ~80% of the clusters are disrupted each decade in time. We investigate the claim that galaxies with high {Sigma}_SFR_ form clusters more efficiently than quiescent systems by determining the fraction of stars in bound clusters ({Gamma}) and the CMF/SFR statistic (CMF is the cluster mass function) for NGC 3256 and comparing the results with those for other galaxies. We find that the CMF/SFR statistic for NGC 3256 agrees well with that found for galaxies with {Sigma}_SFR_ and SFRs that are lower by 1-3 orders of magnitude, but that estimates for {Gamma} are only robust when the same sets of assumptions are applied. Currently, {Gamma} values available in the literature have used different sets of assumptions, making it more difficult to compare the results between galaxies.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/886/99
- Title:
- HST obs. in the region of 3 young LMC SNIa remnants
- Short Name:
- J/ApJ/886/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used two methods to search for surviving companions of Type Ia supernova progenitors in three Balmer-dominated supernova remnants in the Large Magellanic Cloud: 0519-69.0, 0505-67.9 (DEM L71), and 0548-70.4. In the first method, we use the Hubble Space Telescope photometric measurements of stars to construct color-magnitude diagrams (CMDs) and compare positions of stars in the CMDs with those expected from theoretical post-impact evolution of surviving main-sequence or helium star companions. No obvious candidates of surviving companions are identified in this photometric search. Future models for surviving red giant companions or with different explosion mechanisms are needed for thorough comparisons with these observations in order to make more definitive conclusions. In the second method, we use Multi Unit Spectroscopic Explorer observations of 0519-69.0 and DEM L71 to carry out spectroscopic analyses of stars in order to use large peculiar radial velocities as diagnostics of surviving companions. We find a star in 0519-69.0 and a star in DEM L71 moving at radial velocities of 182+/-0km/s and 213+/-0km/s, respectively, more than 2.5{sigma} from the mean radial velocity of the underlying stellar population, 264 and 270km/s, respectively. These stars need higher-quality spectra to investigate their abundances and rotation velocities to determine whether they are indeed surviving companions of the supernova progenitors.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/67
- Title:
- HST obs. of Mira candidates in NGC 4258
- Short Name:
- J/ApJ/857/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present year-long, near-infrared (NIR) Hubble Space Telescope (HST) WFC3 observations of Mira variables in the water megamaser host galaxy NGC 4258. Miras are asymptotic giant branch variables that can be divided into oxygen- (O-) and carbon- (C-) rich subclasses. Oxygen-rich Miras follow a tight (scatter ~0.14mag) period-luminosity relation (PLR) in the NIR and can be used to measure extragalactic distances. The water megamaser in NGC 4258 gives a geometric distance to the galaxy accurate to 2.6% that can serve to calibrate the Mira PLR. We develop criteria for detecting and classifying O-rich Miras with optical and NIR data as well as NIR data alone. In total, we discover 438 Mira candidates that we classify with high confidence as O-rich. Our most stringent criteria produce a sample of 139 Mira candidates that we use to measure a PLR. We use the OGLE-III sample of O-rich Miras in the Large Magellanic Cloud to obtain a relative distance modulus, {mu}_4258_-{mu}_LMC_=10.95+/-0.01 (statistical) +/-0.06 (systematic) mag, that is statistically consistent with the relative distance determined using Cepheids. These results demonstrate the feasibility of discovering and characterizing Miras using the NIR with the HST and the upcoming James Webb Space Telescope and using those Miras to measure extragalactic distances and determine the Hubble constant.
- ID:
- ivo://CDS.VizieR/J/ApJ/889/5
- Title:
- HST obs. of Mira variables in the SNIa host NGC1559
- Short Name:
- J/ApJ/889/5
- Date:
- 17 Jan 2022 11:46:55
- Publisher:
- CDS
- Description:
- We present year-long, near-infrared Hubble Space Telescope (HST) WFC3 observations used to search for Mira variables in NGC 1559, the host galaxy of the Type Ia supernova (SN Ia) SN 2005df. This is the first dedicated search for Miras, highly evolved low-mass stars, in an SNIa host, and subsequently the first calibration of the SN Ia luminosity using Miras in a role historically played by Cepheids. We identify a sample of 115 O-rich Miras with P<400days based on their light-curve properties. We find that the scatter in the Mira period-luminosity relation (PLR) is comparable to Cepheid PLRs seen in SN Ia host galaxies. Using a sample of O-rich Miras discovered in NGC 4258 with HSTF160W and its maser distance, we measure a distance modulus for NGC1559 of {mu}_1559_=31.41+/-0.050(statistical)+/-0.060(systematic)mag. Based on the light curve of the normal, well-observed, low-reddening SN 2005df, we obtain a measurement of the fiducial SN Ia absolute magnitude of M_B_^0^=-19.27+/-0.13mag. With the Hubble diagram of SNe Ia we find H_0_=72.7+/-4.6km/s/Mpc. Combining the calibration from the NGC 4258 megamaser and the Large Magellanic Cloud detached eclipsing binaries gives a best value of H_0_=73.3+/-4.0km/s/Mpc. This result is within 1{sigma} of the Hubble constant derived using Cepheids and multiple calibrating SNe Ia. This is the first of four expected calibrations of the SN Ia luminosity from Miras that should reduce the error in H_0_ via Miras to ~3%. In light of the present Hubble tension and JWST, Miras have utility in the extragalactic distance scale to check Cepheid distances or calibrate nearby SNe in early-type host galaxies that would be unlikely targets for Cepheid searches.
- ID:
- ivo://CDS.VizieR/J/AJ/121/916
- Title:
- HST obs. of NGC 2298, 5897, 6535, and 6626
- Short Name:
- J/AJ/121/916
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HST observations of the core of four galactic globular clusters allowed us to obtain interesting clues about the influence of the environment on the star distribution along the horizontal branch. The chemical composition and the age of the target clusters have been derived through a detailed analysis of the (V, V-I) color-magnitude diagrams. The photometric metallicities have been found in close agreement with the recent spectroscopic determinations.
- ID:
- ivo://CDS.VizieR/J/ApJ/902/26
- Title:
- HST opt. & H-band obs. of Cepheids in NGC4151
- Short Name:
- J/ApJ/902/26
- Date:
- 14 Mar 2022 07:44:50
- Publisher:
- CDS
- Description:
- We derive a distance of 15.8+/-0.4Mpc to the archetypal Seyfert 1 galaxy NGC 4151 based on the near-infrared Cepheid period-luminosity relation and new Hubble Space Telescope multiband imaging. This distance determination, based on measurements of 35 long-period (P>25d) Cepheids, will support the absolute calibration of the supermassive black hole mass in this system, as well as studies of the dynamics of the feedback or feeding of its active galactic nucleus.
- ID:
- ivo://CDS.VizieR/J/AJ/130/2043
- Title:
- HST paired and isolated galaxies
- Short Name:
- J/AJ/130/2043
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare the structural properties of two classes of galaxies at intermediate redshift: those in dynamically close galaxy pairs, and those that are isolated. Both samples are selected from the Canadian Network for Observational Cosmology field galaxy redshift survey (CNOC2, Cat. <J/ApJS/129/475>) and have redshifts in the range 0.1<z<0.6. Hubble Space Telescope WFPC2 images were acquired as part of a snapshot survey and were used to measure bulge fraction and asymmetry for these galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/881/42
- Title:
- HST phot. & GMOS spectra of Lynx E & W clusters
- Short Name:
- J/ApJ/881/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Few detailed investigations of stellar populations in passive galaxies beyond z~1 are based on deep spectroscopic observations, due to the difficulty in obtaining such data. We present a study of stellar populations, structure, and mass-to-light ratios (M/L) of a large sample of bulge-dominated galaxies in the two z=1.27 clusters Lynx E and Lynx W, based on deep ground-based optical spectroscopy combined with imaging from the Hubble Space Telescope. We find that Lynx E has a well-defined core of red passive galaxies, while Lynx W lacks such a core. If all the sample galaxies evolve similarly in size from z=1.27 to the present, the data would allow only 0.1dex size growth at a fixed dynamical mass. However, to link the Lynx central galaxies to brightest cluster galaxies similar to those of low-redshift clusters, the Lynx galaxies would have to grow by at least a factor 5, possibly through major merging. The M/L ratios and the Balmer absorption lines of the Lynx galaxies are consistent with passive evolution of the stellar populations from z=1.27 to the present and support ages of 1-3Gyr. The galaxies in the outskirts of the clusters contain younger stellar populations than found in the cluster cores. However, when evolved passively to z~0 both populations are consistent with the observed populations in the Coma cluster galaxies. The bulge-dominated emission line galaxies in the clusters are dominated by stellar populations with subsolar metallicities. Thus, additional enrichment of these is required to produce Coma-like stellar populations by z~0.
- ID:
- ivo://CDS.VizieR/J/AJ/143/74
- Title:
- HST photometry in 6 dwarf galaxies
- Short Name:
- J/AJ/143/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive study of young stellar populations in six dwarf galaxies in or near the Local Group: Phoenix, Pegasus, Sextans A, Sextans B, WLM, and NGC 6822. Their star-forming regions, selected from GALEX wide-field far-UV imaging, were imaged (at sub-pc resolution) with the WFPC2 camera on board the Hubble Space Telescope (HST) in six bandpasses from far-UV to IR to detect and characterize their hot massive star content. This study is part of HST treasury survey program HST-GO-11079; the general data characteristics and reduction procedures are detailed in this paper and results are presented for the first six galaxies. From a total of 180 HST images, we provide catalogs of the multi-band stellar photometry and derive the physical parameters of massive stars by analyzing it with model-atmosphere colors. We use the results to infer ages, number of massive stars, extinction, and spatial characteristics of the young stellar populations. The hot massive star content varies largely across our galaxy sample, from an inconspicuous presence in Phoenix and Pegasus to the highest relative abundance of young massive stars in Sextans A and WLM. Albeit to a largely varying extent, most galaxies show a very young population (a few Myrs, except for Phoenix), and older ones (a few 10^7^ years in Sextans A, Sextans B, NGC 6822, and WLM, ~10^8^yr in Phoenix and Pegasus), suggesting discrete bursts of recent star formation in the mapped regions. The hot massive star content (indicative of the young populations) broadly correlates with the total galaxy stellar mass represented by the integrated optical magnitude, although it varies by a factor of ~3 between Sextans A, WLM, and Sextans B, which have similar M_V_. Extinction properties are also derived.
- ID:
- ivo://CDS.VizieR/J/A+A/532/A147
- Title:
- HST photometry in extragalactic star clusters
- Short Name:
- J/A+A/532/A147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present colour-magnitude diagrams (CMDs) for a sample of seven young massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705 and NGC 5236. The clusters have ages in the range 5-50 million years and masses of 10^5^-10^6^M_{sun}_. Although crowding prevents us from obtaining photometry in the inner regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters, along with the brighter main sequence stars. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. This spread can be reproduced by including an age spread of 10-30 million years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role.
