- ID:
- ivo://CDS.VizieR/J/AJ/125/1696
- Title:
- Star-forming knots in NGC 3395/3396
- Short Name:
- J/AJ/125/1696
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained ultraviolet and visible wavelength images for the central regions of the interacting galaxies NGC 3395 and NGC 3396, using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The images show many isolated sources of ultraviolet emission produced by young star-forming regions (knots). The FWHM of most of the knots in both galaxies is <=20pc. Far-UV flux distributions for the complete sample of knots can be fitted with a power law with exponent {alpha}=-1.20+/-0.35 for NGC 3395 and a power law with exponent {alpha}=-0.69+/-0.21 for NGC 3396. Comparison with models from Leitherer et al. indicates that the ages of most of the knots are <=80Myr. Reddening of the knots ranges from E(B-V)=0.0 to E(B-V)=0.3mag, indicating variable amounts of dust in these regions. Almost all the knots have masses less than 10^6^M_{sun}_. Many of the knots are probably bound and at least six knots are good proto-globular cluster candidates. There are no significant differences in the fluxes, sizes, and ages of the knots in the two galaxies. The average mass of the knots in NGC 3395 is an order of magnitude less than the average mass of the knots in NGC 3396. There is no obvious correlation between the age of a knot and its position the galaxy.
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- ID:
- ivo://CDS.VizieR/J/AJ/127/1360
- Title:
- Star-forming knots in NGC 4194 center
- Short Name:
- J/AJ/127/1360
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report high-resolution ultraviolet and visible-wavelength imaging of the blue compact galaxy NGC 4194 (the Medusa) using the Hubble Space Telescope. A complete sample of 38 UV-bright knots is identified.
- ID:
- ivo://CDS.VizieR/J/ApJ/730/88
- Title:
- Star-forming regions in NGC 6822 from UV data
- Short Name:
- J/ApJ/730/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We characterize the star formation in the low-metallicity galaxy NGC 6822 over the past few hundred million years, using GALEX far-UV (FUV, 1344-1786{AA}) and near-UV (NUV, 1771-2831{AA}) imaging, and ground-based H{alpha} imaging. From the GALEX FUV image, we define 77 star-forming (SF) regions with area >860pc^2^, and surface brightness <~26.8 mag (AB) arcsec^-2^, within 0.2{deg} (1.7kpc) of the center of the galaxy. We estimate the extinction by interstellar dust in each SF region from resolved photometry of the hot stars it contains: E(B-V) ranges from the minimum foreground value of 0.22mag up to 0.66+/-0.21mag. The integrated FUV and NUV photometry, compared with stellar population models, yields ages of the SF complexes up to a few hundred Myr, and masses from 2x10^2^M_{sun}_ to 1.5x10^6^M_{sun}_. The derived ages and masses strongly depend on the assumed type of interstellar selective extinction, which we find to vary across the galaxy. The total mass of the FUV-defined SF regions translates into an average star formation rate (SFR) of 1.4x10^-2^M_{sun}_/yr over the past 100Myr, and SFR=1.0x10^-2^M_{sun}_/yr in the most recent 10Myr. The latter is in agreement with the value that we derive from the H{alpha} luminosity, SFR=0.008M_{sun}_/yr. The SFR in the most recent epoch becomes higher if we add the SFR=0.02M_{sun}_/yr inferred from far-IR measurements, which trace star formation still embedded in dust (age <~ a few Myr).
- ID:
- ivo://CDS.VizieR/J/ApJS/234/35
- Title:
- Stellar population synthesis of clumps
- Short Name:
- J/ApJS/234/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have identified 1027 star-forming complexes in a sample of 46 galaxies from the Spirals, Bridges, and Tails (SB&T) sample of interacting galaxies, and 693 star-forming complexes in a sample of 38 non-interacting spiral (NIS) galaxies in 8{mu}m observations from the Spitzer Infrared Array Camera. We have used archival multi-wavelength UV-to IR observations to fit the observed spectral energy distribution of our clumps with the Code Investigating GALaxy Emission using a double exponentially declined star formation history. We derive the star formation rates (SFRs), stellar masses, ages and fractions of the most recent burst, dust attenuation, and fractional emission due to an active galactic nucleus for these clumps. The resolved star formation main sequence holds on 2.5kpc scales, although it does not hold on 1kpc scales. We analyzed the relation between SFR, stellar mass, and age of the recent burst in the SB&T and NIS samples, and we found that the SFR per stellar mass is higher in the SB&T galaxies, and the clumps are younger in the galaxy pairs. We analyzed the SFR radial profile and found that the SFR is enhanced through the disk and in the tidal features relative to normal spirals.
- ID:
- ivo://CDS.VizieR/J/A+A/654/A135
- Title:
- 12 strong galactic bars CO spectra
- Short Name:
- J/A+A/654/A135
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- While some galactic bars show recent massive star formation (SF) along them, some others present a lack of it. Whether bars with low level of SF are a consequence of low star formation efficiency, low gas inflow rate, or dynamical effects, remains a matter of debate. In order to study the physical conditions that enable or prevent SF, we perform a multi-wavelength analysis of 12 strongly barred galaxies with total stellar masses log10(M*/M_{sun}_){in}[10.2,11], chosen to host different degrees of SF along the bar major axis without any prior condition on gas content. We observe the CO(1-0) and CO(2-1) emission within bars with the IRAM-30m telescope (beam sizes of 1.7-3.9kpc and 0.9-2.0kpc, respectively; 7-8 pointings per galaxy on average). We estimate molecular gas masses (Mmol) from the CO(1-0) and CO(2-1) emissions. SF rates (SFR) are calculated from GALEX near-ultraviolet (UV) and WISE 12um images within the beam-pointings, covering the full bar extent (SFRs are also derived from far-UV and 22um). Results. We detect molecular gas along the bars of all probed galaxies. Molecular gas and SFR surface densities span the ranges log10({Sigma}_mol_/[M_{sun}_/pc^2^]){in}[0.4,2.4] and log10({Sigma}_SFR_/[M_{sun}_/pc/kpc^2^]){in}[-3.25,-0.75], respectively. The star formation efficiency (SFE=SFR/Mmol) in bars varies between galaxies by up to an order of magnitude (SFE{in}[0.1,1.8]Gyr^-1^). On average, SFEs are roughly constant along bars. SFEs are not significantly different from the mean value in spiral galaxies reported in the literature (~0.43Gyr^-1^), regardless of whether we estimate Mmol from CO(1-0) or CO(2-1). Interestingly, the higher the total stellar mass of the host galaxy, the lower the SFE within their bars. In particular, the two galaxies in our sample with lowest SFE and {Sigma}_SFR_ (NGC 4548 and NGC 5850, SFE<=0.25Gyr^-1^, {Sigma}_SFR_<=10^-2.25^M_{sun}_/yr/kpc^2^, M*<=10^10.7^M_{sun}_) are also the ones hosting massive bulges and signs of past interactions with nearby companions. We present a statistical analysis of the SFE in bars for a sample of 12 galaxies. The SFE in strong bars is not systematically inhibited (either in the central, mid- or end-parts of the bar). Both environmental and internal quenching are likely responsible for the lowest SFEs reported in this work.
- ID:
- ivo://CDS.VizieR/J/other/ATel/5200
- Title:
- Swift Galactic Plane Survey sourcelist v3
- Short Name:
- J/other/ATel/520
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Swift Galactic Plane Survey team report the detection of 248 point-like X-ray sources (0.3-10keV) in observations covering the final 40% of our survey area (see also 2012ATel.3951....1R and 2012ATel.4318....1R). The listed sources are those we consider to be robust detections at the current time.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/66
- Title:
- Swift observations of Mrk 421. I. 2005-2008
- Short Name:
- J/ApJ/854/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present detailed results of Swift observations of the nearby TeV-detected blazar Mrk 421, based on the rich archival data obtained during 2005 March-2008 June. The best fits of the 0.3-10keV spectra were mainly obtained using the log-parabolic model, yielding low spectral curvatures expected in the case of the efficient stochastic acceleration of particles. During strong X-ray flares, the position of the synchrotron spectral energy distribution peak E_p_ was beyond 8keV for 41 spectra, while it sometimes was situated at the UV frequencies in quiescent states. The photon index at 1 keV exhibited a broad range, and the values a<1.70 were observed during the strong flares, hinting at the possible presence of a jet hadronic component. The spectral parameters were correlated in some periods, expected in the framework of the first- and second-order Fermi accelerations of X-ray emitting particles, as well as in the case of turbulence spectrum. The 0.3-10keV flux and spectral parameters sometimes showed very fast variability down to the fluctuations by 6-20% in 180-960s, possibly related to the small-scale turbulent areas containing strongest magnetic fields. X-ray and very high-energy fluxes often showed correlated variability, although several occurrences of more complicated variability patterns are also revealed, indicating that the multifrequency emission of Mrk 421 could not be generated in a single zone.
- ID:
- ivo://CDS.VizieR/J/ApJ/858/68
- Title:
- Swift obs. of Mrk 421 in selected epochs. II.
- Short Name:
- J/ApJ/858/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from a detailed spectral and timing study of Mrk 421 based on the rich archival Swift data obtained during 2009-2012. Best fits of the 0.3-10keV spectra were mostly obtained using the log-parabolic model showing the relatively low spectral curvature that is expected in the case of efficient stochastic acceleration of particles. The position of the synchrotron spectral energy density peak E_p_ of 173 spectra is found at energies higher than 2keV. The photon index at 1 keV exhibited a very broad range of values a=1.51-3.02, and very hard spectra with a<1.7 were observed during the strong X-ray flares, hinting at a possible hadronic jet component. The spectral parameters varied on diverse timescales and showed a correlation in some periods, which is expected in the case of first- and second-order Fermi acceleration. The 0.3-10keV flux showed strong X-ray flaring activity by a factor of 3-17 on timescales of a few days-weeks between the lowest historical state and that corresponding to a rate higher than 100ct/s. Moreover, 113 instances of intraday variability were revealed, exhibiting shortest flux-doubling/halving times of about 1.2hr, as well as brightenings by 7%-24% in 180-720 s and declines by 68%-22% in 180-900s. The X-ray and very high-energy fluxes generally showed a correlated variability, although one incidence of a more complicated variability was also detected, indicating that the multifrequency emission of Mrk 421 could not be generated in a single zone.
- ID:
- ivo://CDS.VizieR/J/ApJ/828/3
- Title:
- Swift obs. of the superluminous SNI ASASSN-15lh
- Short Name:
- J/ApJ/828/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present and discuss ultraviolet and optical photometry from the Ultraviolet/Optical Telescope, X-ray limits from the X-Ray Telescope on Swift, and imaging polarimetry and ultraviolet/optical spectroscopy with the Hubble Space Telescope, all from observations of ASASSN-15lh. It has been classified as a hydrogen-poor superluminous supernova (SLSN I), making it more luminous than any other supernova observed. ASASSN-15lh is not detected in the X-rays in individual or co-added observations. From the polarimetry we determine that the explosion was only mildly asymmetric. We find the flux of ASASSN-15lh to increase strongly into the ultraviolet, with an ultraviolet luminosity 100 times greater than the hydrogen-rich, ultraviolet-bright SLSN II SN 2008es. We find that objects as bright as ASASSN-15lh are easily detectable beyond redshifts of ~4 with the single-visit depths planned for the Large Synoptic Survey Telescope. Deep near-infrared surveys could detect such objects past a redshift of ~20, enabling a probe of the earliest star formation. A late rebrightening-most prominent at shorter wavelengths-is seen about two months after the peak brightness, which is itself as bright as an SLSN. The ultraviolet spectra during the rebrightening are dominated by the continuum without the broad absorption or emission lines seen in SLSNe or tidal disruption events (TDEs) and the early optical spectra of ASASSN-15lh. Our spectra show no strong hydrogen emission, showing only Ly{alpha} absorption near the redshift previously found by optical absorption lines of the presumed host. The properties of ASASSN-15lh are extreme when compared to either SLSNe or TDEs.
- ID:
- ivo://CDS.VizieR/J/ApJ/870/123
- Title:
- Swift optical & UV flux of four AGNs
- Short Name:
- J/ApJ/870/123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ~200-350 times in 0.3-10keV X-ray and six UV/optical bands. Uniform reduction and cross-correlation analysis of these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for the lamp-post reprocessing model in which variations in a central X-ray corona drive and power those in the surrounding accretion disk. (2) The UV/optical interband lags are generally consistent with {tau}{propto}{lambda}^4/3^ as predicted by the centrally illuminated thin accretion disk model. While the average interband lags are somewhat larger than predicted, these results alone are not inconsistent with the thin disk model given the large systematic uncertainties involved. (3) The one exception is the U band lags, which are on average a factor of ~2.2 larger than predicted from the surrounding band data and fits. This excess appears to be due to diffuse continuum emission from the broad-line region (BLR). The precise mixing of disk and BLR components cannot be determined from these data alone. The lags in different AGN appear to scale with mass or luminosity. We also find that there are systematic differences between the uncertainties derived by Just Another Vehicle for Estimating Lags In Nuclei (JAVELIN) versus more standard lag measurement techniques, with JAVELIN reporting smaller uncertainties by a factor of 2.5 on average. In order to be conservative only standard techniques were used in the analyses reported herein.