- ID:
- ivo://CDS.VizieR/J/A+A/623/A65
- Title:
- Multiphotometry of M31 outer halo globular clusters
- Short Name:
- J/A+A/623/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present photometry of 53 globular clusters (GCs) in the M31 outer halo, including the GALEX FUV and NUV, SDSS ugriz, 15 intermediate-band filters of BATC, and 2MASS JHKs bands. By comparing the multicolour photometry with stellar population synthesis models, we determine the metallicities, ages, and masses for these GCs, aiming to probe the merging/accretion history of M31. We find no clear trend of metallicity and mass with the de-projected radius. The halo GCs with age younger than ~8Gyr are mostly located at the de-projected radii around 100kpc, but this may be due to a selection effect. We also find that the halo GCs have consistent metallicities with their spatially-associated substructures, which provides further evidence of the physical association between them. Both the disk and halo GCs in M31 show a bimodal luminosity distribution. However, we should emphasize that there are more faint halo GCs which are not being seen in the disk. There are more faint halo GCs than the disk ones, and these faint GCs constitute the fainter part in the luminosity function. The bimodal luminosity function of the halo GCs may reflect different origin or evolution environment in their original hosts. The M31 halo GCs includes one intermediate metallicity group (-1.5<[Fe/H]<-0.4) and one metal-poor group ([Fe/H]<-1.5), while the disk GCs have one metal-rich group more. There are considerable differences between the halo GCs in M31 and the Milky Way (MW). The total number of M31 GCs is approximately three times more numerous than that of the MW, however, M31 has about six times the number of halo GCs in the MW. Compared to M31 halo GCs, the Galactic halo ones are mostly metal-poor. Both the numerous halo GCs and the higher-metallicity component are suggestive of an active merger history of M31.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/857/64
- Title:
- Multiwavelength catalog in the SEP field. II.
- Short Name:
- J/ApJ/857/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For a sample of star-forming galaxies in the redshift interval 0.15<z<0.3, we study how both the relative strength of the active galactic nucleus (AGN) infrared emission, compared to that due to the star formation (SF), and the numerical fraction of AGNs change as a function of the total stellar mass of the hosting galaxy group (M_group_^*^) between 10^10.25^ and 10^11.9^M_{sun}_. Using a multicomponent spectral energy distribution SED fitting analysis, we separate the contribution of stars, AGN torus, and star formation to the total emission at different wavelengths. This technique is applied to a new multiwavelength data set in the SIMES field (23 not-redundant photometric bands), spanning the wavelength range from the UV (GALEX) to the far-IR (Herschel) and including crucial AKARI and WISE mid-IR observations (4.5{mu}m<{lambda}<24{mu}m), where the black hole thermal emission is stronger. This new photometric catalog, which includes our best photo-z estimates, is released through the NASA/IPAC Infrared Science Archive (IRSA). Groups are identified through a friends-of-friends algorithm (~62% purity, ~51% completeness). We identified a total of 45 galaxies requiring an AGN emission component, 35 of which are in groups and 10 in the field. We find the black hole accretion rate (BHAR){prop.to}(M_group_^*^)^1.21+/-0.27^ and (BHAR/SFR) {\prop} (M_group_^*^)^1.04+/- 0.24^, while, in the same range of M_group_^*^, we do not observe any sensible change in the numerical fraction of AGNs. Our results indicate that the nuclear activity (i.e., the BHAR and the BHAR/SFR ratio) is enhanced when galaxies are located in more massive and richer groups.
- ID:
- ivo://CDS.VizieR/J/ApJ/586/794
- Title:
- Multiwavelength luminosities of galaxies
- Short Name:
- J/ApJ/586/794
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I have assembled a diverse sample of galaxies from the literature with far-ultraviolet (FUV), optical, infrared (IR), and radio luminosities to explore the calibration of radio-derived and IR-derived star formation (SF) rates and the origin of the radio-IR correlation. By comparing the 8-1000{mu}m IR, which samples dust-reprocessed starlight, with direct stellar FUV emission, I show that the IR traces most of the SF in luminous ~L* galaxies but traces only a small fraction of the SF in faint ~0.01L* galaxies. If radio emission were a perfect SF rate indicator, this effect would cause easily detectable curvature in the radio-IR correlation. Yet, the radio-IR correlation is nearly linear. This implies that the radio flux from low-luminosity galaxies is substantially suppressed, compared to brighter galaxies. This is naturally interpreted in terms of a decreasing efficiency of nonthermal radio emission in faint galaxies. Thus, the linearity of the radio-IR correlation is a conspiracy: both indicators underestimate the SF rate at low luminosities. SF rate calibrations that take into account this effect are presented, along with estimates of the random and systematic error associated with their use.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/81
- Title:
- Multiwavelength survey of HII regions in NGC 300
- Short Name:
- J/ApJ/789/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 H II regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250pc scales using pointed CO(J=2-1) observations with the Atacama Pathfinder Experiment telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ~10^5^M_{sun}_ to 7x10^5^M_{sun}_. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine Galaxy Evolution Explorer far-ultraviolet, Spitzer 24{mu}m, and H{alpha} narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates (SFRs) that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our H II region targets. We find a characteristic gas depletion time of 230Myr at 250pc scales in NGC 300, more similar to the results obtained for Milky Way giant molecular clouds than the longer (>2Gyr) global depletion times derived for entire galaxies and kiloparsec-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star-forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A33
- Title:
- Nearby radio galaxies FUV to MIR properties
- Short Name:
- J/A+A/581/A33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate whether the far-UV continuum of nearby radio galaxies is due solely to the parent galaxy that passively evolves, or if it reveals evidence for the presence of other star-forming or non-stellar components. If the UV excess is due to an additional radiation component, we compare this with other properties such as radio power, optical spectral type (e.g. high- and low-excitation galaxies), and the strength of the emission lines. We also discuss the possible correlation between the ultraviolet flux, IR properties, and the central black hole mass. We used a sample of low-luminosity B2 radio galaxies and a small sample of higher luminosity 3C radio galaxies at comparable redshift (z<0.2). Spectral energy distributions (SEDs) were constructed using a number of on-line databases that are freely available now: GALEX, SDSS, 2MASS, and WISE. These were compared with model SEDs of early-type galaxies with passively evolving stellar populations at various ages (typically 0.5-1.3x10^9^ years). We established whether a second component was needed to obtain a satisfactory fit with the observed overall SED. We introduce the parameter XUV, which measures the excess slope of the UV continuum between 4500 and 2000{AA} with respect to the UV radiation produced by the underlying old galaxy component. We find that the UV excess as measured by XUV is usually small or absent in low-luminosity (FR I) sources, but sets in abruptly at the transition radio power, above which we find mostly FRII sources. XUV behaves very similarly to the strength of the optical emission lines (in particular H{alpha}). Below P_1.4GHz_<10^24^W/Hz XUV is close to zero. XUV correlates strongly with the H{alpha} line strength, but only in sources with strong H{alpha} emission. We discuss whether the line emission might be due to photoionization by radiation from the parent galaxy, possibly with additional star formation, or if it requires the presence of a non-stellar active galactic nucleus component. XUV and the slope of the mid-IR are strongly correlated, as measured by the WISE bands in the interval 3.4 to 22{mu}m, in the sense that sources with a strong UV excess also have stronger IR emission. There is an inverse correlation between XUV and central black hole mass: the M_BH_ of objects with strong UV excess is on average two to three times less massive than that of objects without UV excess. Low-luminosity radio galaxies tend to be more massive and contain more massive black holes.
- ID:
- ivo://CDS.VizieR/J/MNRAS/402/436
- Title:
- New Dwarf novae in SDSS, GALEX and astrom. cat.
- Short Name:
- J/MNRAS/402/436
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By cross-matching blue objects from the Sloan Digital Sky Survey with Galaxy Evolution Explorer and the astrometric catalogues USNO-B1.0, GSC2.3 and CMC14, 64 new dwarf nova candidates with one or more observed outbursts have been identified. 14 of these systems are confirmed as cataclysmic variables through existing and follow-up spectroscopy. A study of the amplitude distribution and an estimate of the outburst frequency of these new dwarf novae and those discovered by the Catalina Real-time Transient Survey indicate that besides systems that are faint because they are farther away, there also exists a population of intrinsically faint dwarf novae with rare outbursts.
- ID:
- ivo://CDS.VizieR/J/MNRAS/457/3396
- Title:
- New hot subdwarf stars
- Short Name:
- J/MNRAS/457/3396
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent massive sky surveys in different bandwidths are providing new opportunities to modern astronomy. The Virtual Observatory (VO) represents the adequate framework to handle the huge amount of information available and filter out data according to specific requirements. In this work, we applied a selection strategy to find new, uncatalogued hot subdwarfs making use of VO tools. We used large area catalogues like GALEX, Sloan Digital Sky Survey (SDSS), SuperCosmos and Two Micron All Sky Survey (2MASS) to retrieve photometric and astrometric information of stellar objects. To these objects, we applied colour and proper motion filters, together with an effective temperature cutoff, aimed at separating hot subdwarfs from other blue objects such as white dwarfs, cataclysmic variables or main-sequence OB stars. As a result, we obtained 437 new, uncatalogued hot subdwarf candidates. Based on previous results, we expect our procedure to have an overall efficiency of at least 80 per cent. Visual inspection of the 68 candidates with SDSS spectrum showed that 65 can be classified as hot subdwarfs: 5 sdOs, 25 sdOBs and 35 sdBs. This success rate above 95 per cent proves the robustness and efficiency of our methodology. The spectral energy distribution of 45 per cent of the subdwarf candidates showed infrared excesses, a signature of their probable binary nature. The stellar companions of the binary systems so detected are expected to be late-type main-sequence stars. A detailed determination of temperatures and spectral classification of the cool companions will be presented in a forthcoming work.
- ID:
- ivo://CDS.VizieR/J/PASP/130/H4203
- Title:
- Newly spectroscopically confirmed DB white dwarfs
- Short Name:
- J/PASP/130/H4203
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a machine learning (ML) method, we mine DB white dwarfs (DBWDs) from the Sloan Digital Sky Survey (SDSS) Data Release (DR) 12 and DR14. The ML method consists of two parts: feature extraction and classification. The least absolute shrinkage and selection operator (LASSO) is used for the spectral feature extraction by comparing high quality data of a positive sample group with negative sample groups. In both the training and testing sets, the positive sample group is composed of a selection of 300 known DBWDs, while the negative sample groups are obtained from all types of SDSS spectra. In the space of the LASSO detected features, a support vector machine is then employed to build classifiers that are used to separate the DBWDs from the non-DBWDs for each individual type. Depending on the classifiers, the DBWD candidates are selected from the entire SDSS data set. After visual inspection, 2808 spectra (2029 objects) are spectroscopically confirmed. By checking the samples with the literature, there are 58 objects with 60 spectra that are newly identified, including a newly discovered AM CVn. Finally, we measure their effective temperatures (T_eff_), surface gravities (log g), and radial velocities, before compiling them into a catalog.
- ID:
- ivo://CDS.VizieR/J/AJ/117/1708
- Title:
- NGC 1741 HST photometry
- Short Name:
- J/AJ/117/1708
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Hubble Space Telescope (HST) Faint Object Camera (FOC) ultraviolet (UV) and WFPC2 optical images in conjunction with UV spectroscopic observations taken with the Goddard High Resolution Spectrograph to examine the star formation history and properties of the interacting galaxy system NGC 1741 in the Hickson Compact Group 31. The high spatial resolution afforded by HST has allowed us to identify a large number of starburst knots, or "superstar clusters" (SSCs), in the starburst regions of this system. Photometry of these SSCs in the UV and optical bands indicates that most of these objects have ages of a few Myr, with a few up to ~100Myr, and masses between 10^4^ and 10^6^M_{sun}_. The estimated age is confirmed by a spectral synthesis analysis of one knot for which we have obtained a UV spectrum. The V-band luminosity function of the SSCs is well represented by a power law {Phi}(L)~L^-{alpha}^ with an index of -1.85, with no evidence of a turnover brighter than the completeness limit. These properties are in good agreement with those found for SSCs in other starburst galaxies. Our results support the suggestion that some of these SSCs may be extremely young globular clusters formed in a relatively recent starburst episode that has been triggered by a merger event.
- ID:
- ivo://CDS.VizieR/J/MNRAS/423/2901
- Title:
- NGC 6752 multiwavelength survey
- Short Name:
- J/MNRAS/423/2901
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a multiwavelength (far-ultraviolet to I band) survey of the stellar populations of the globular cluster NGC 6752, using Space Telescope Imaging Spectrograph (STIS, FUV, 2001/03/01), Advanced Camera for Surveys (ACS, VI on 2006/06/24) and Wide Field Camera 3 (WFC3, NUV on 2010/07/31, 2010/08/07 and 2010/08/21, and UB on 2010/05/1-5) on board the Hubble Space Telescope. We have confirmed that two previously identified cataclysmic variable (CV) candidates are, in fact, dwarf novae which underwent outbursts during our observations. We have also identified previously unknown optical counterparts to two X-ray sources.
