- ID:
- ivo://CDS.VizieR/J/ApJ/733/46
- Title:
- Velocity measurements in Segue 1
- Short Name:
- J/ApJ/733/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity measurements for 98.2% of the stars within 67pc (10', or 2.3 half-light radii) of the center of Segue 1 that have colors and magnitudes consistent with membership, down to a magnitude limit of r=21.7. Based on photometric, kinematic, and metallicity information, we identify 71 stars as probable Segue 1 members, including some as far out as 87pc. After correcting for the influence of binary stars using repeated velocity measurements, we determine a velocity dispersion of 3.7^+1.4^_-1.1_km/s. The mass within the half-light radius is 5.8^+8.2^_-3.1_x10^5^M_{sun}_. The stellar kinematics of Segue 1 require very high mass-to-light ratios unless the system is far from dynamical equilibrium, even if the period distribution of unresolved binary stars is skewed toward implausibly short periods. With a total luminosity less than that of a single bright red giant and a V-band mass-to-light ratio of 3400M_{sun}_/L_{sun}_, Segue 1 is the darkest galaxy currently known.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/853/114
- Title:
- Vertical population gradients in NGC 891. I.
- Short Name:
- J/ApJ/853/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have measured vertical and radial stellar population gradients in NGC 891. We compare these gradients to those known for the Milky Way from studies of resolved stars. Optical spectroscopic measurements extend spatially from the disk midplane up to 2.6kpc in height and out to a radius of 12kpc on both sides of the galaxy. Data were acquired with {nabla}Pak, a variable-pitch fiber integral field unit (IFU) on the WIYN telescope. We describe the laboratory and on-sky performance of {nabla}Pak, as well as modifications to the standard observational and analysis procedures necessary to calibrate data taken with this unique IFU. {nabla}Pak has a mean throughput of 80% at 5500{AA}. To achieve an estimated precision of 10% in light-weighted mean age and metallicity, we define a set of spatial apertures in radius and height in which spectra are binned to achieve a signal-to-noise ratio of ~20{AA}^-1^. We use spectral indices to measure age, metallicity, and abundance, indicating that NGC 891's stellar populations have 0.2<Z/Z_{sun}_<1 and +0.2dex {alpha}-enhancement on average. We find a clear transition from young (<3-5Gyr) to old (>7Gyr) stellar populations at 0.4kpc, roughly the scale height of the thin disk. We also find a slight trend toward younger populations at larger radii, consistent with flaring in an inside-out disk formation scenario. The vertical age gradient in NGC 891 is in remarkable qualitative agreement with a model for disk heating tuned to studies of the Milk Way's solar cylinder.
- ID:
- ivo://CDS.VizieR/J/A+A/389/795
- Title:
- Vertical structure of edge-on galaxies
- Short Name:
- J/A+A/389/795
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To analyze the vertical structure of edge-on galaxies, we have used images of a large uniform sample of flat galaxies that have been taken during the 2MASS all-sky survey. The photometric parameters, such as the radial scale length, the vertical scale height, and the deprojected central surface brightness of galactic disks have been obtained. We find a strong correlation between the central surface brightness and the ratio of the vertical scale height to the vertical scale length: the thinner the galaxy, the lower the central surface brightness of its disk. The vertical scale height does not increase systematically with the distance from the galaxy center in the frames of this sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/26
- Title:
- Very low-z SDSS galaxies with H{alpha} emission
- Short Name:
- J/ApJ/765/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Strong H{alpha} emitters (HAEs) dominate the z~4 Lyman-break galaxy (LBG) population. We have identified local analogs of these HAEs using the Sloan Digital Sky Survey. At z<0.4, only 0.04% of the galaxies are classified as HAEs with H{alpha} equivalent widths (>~500{AA}) comparable to that of z~4 HAEs. Local HAEs have lower stellar mass and lower ultraviolet (UV) luminosity than z~4 HAEs, yet the H{alpha}-to-UV luminosity ratio, as well as their specific star formation rate, is consistent with that of z~4 HAEs, indicating that they are scaled-down versions of high-z star-forming galaxies. Compared to the previously studied local analogs of LBGs selected using rest-frame UV properties, local HAEs show similar UV luminosity surface density, weaker D_n_(4000) break, lower metallicity, and lower stellar mass. This implies that the local HAEs are less evolved galaxies than the traditional Lyman break analogs. In the stacked spectrum, local HAEs show a significant He II{lambda}4686 emission line suggesting a population of hot, massive stars similar to that seen in some Wolf-Rayet galaxies. Low [N II]/[O III] line flux ratios imply that local HAEs are inconsistent with being systems that host bright active galactic nuclei. Instead, it is highly likely that local HAEs are galaxies with an elevated ionization parameter, either due to a high electron density or large escape fraction of hydrogen ionizing photons as in the case of Wolf-Rayet galaxies.
4025. Very Luminous Galaxies
- ID:
- ivo://CDS.VizieR/J/A+A/408/905
- Title:
- Very Luminous Galaxies
- Short Name:
- J/A+A/408/905
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The most luminous galaxies in the blue passband have a larger correlation amplitude than L* galaxies. They do not appear to be preferentially located in rich clusters or groups, but a significant fraction of them seem to be in systems which include fainter members. We present an analysis of fields centered on 18 Very Luminous Galaxies (M_B_<=-21) selected from the Southern Sky Redshift Survey 2 (Cat. <J/AJ/116/1>, based on new observations and public data of the 2dF Galaxy Redshift Survey (Cat. <VII/226>); we present also additional data on a CfA VLG and on Arp 127.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/521
- Title:
- Very luminous IRAS galaxies spectra.
- Short Name:
- J/A+AS/127/521
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the results of spectral observations for the largest complete sample of very luminous IRAS galaxies obtained to date. The sample consists of those 73 objects for which log(L_IR_/L_sun_)>=11.5 (H0=50 km/s/Mpc, q0=0.5) and mag<=15.5, and was extracted from the 2Jy IRAS redshift catalog (Cat. <II/174>). All spectra were obtained using 2.16m telescope of Beijing Astronomical Observatory during the years 1994-1996. A total of 123 galaxy spectra were obtained with spectral ranges of 4400A to 7100A and 3500A to 8100A at resolutions of 11.2A and 9.3A respectively. In addition to the 73 spectra for sample galaxies, we also present spectra for ten non-sample galaxies and a further 40 for the companions of sample galaxies. The data presented include nuclear spectrum and the parameters describing the emission lines, absorption lines and continua as well as DSS images and environmental parameters.
- ID:
- ivo://CDS.VizieR/J/A+AS/132/181
- Title:
- Very luminous IRAS galaxies spectra. II.
- Short Name:
- J/A+AS/132/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectroscopic observations of a sample of 73 very luminous IRAS galaxies (log(L_IR_/L_{sun}_)>=11.5 for H_0_=50km/s/Mpc, q_0_=0.5) from the 2Jy redshift survey catalogue were carried out using the 2.16m telescope at the Beijing Astronomical Observatory. The observational data, including the optical images (extracted from Digital Sky Survey) and spectra for these galaxies, are presented in paper I (Wu et al., 1998, Cat. <J/A+AS/127/521>). In this paper, we give the spectral and morphological classifications for these very luminous IRAS galaxies (VLIRGs). We show that about 60% of VLIRGs exhibit AGN-like spectra (Seyfert 1s, Seyfert 2s, LINER-like galaxies). This fraction goes up to 82% for the ultraluminous IRAS galaxies (ULIRGs) subsample (Log(L_IR_/ L_{sun}_)>=12.0). 56% of the VLIRGs show strong interaction or merging signatures; this fraction rises to 91% for the ULIRGs. These statistical results strongly suggest that interaction triggers nuclear activities and enhances the infrared luminosity. We find that LINER and a mixture type which have optical properties of both HII galaxies and LINERs could be at the transition stage from infrared luminous HII galaxies to AGNs; their main energy production is from starbursts as well as AGNs. Both infrared luminosities and Ha equivalent widths increase dramatically as nuclear separations between VLIRGs and their nearest neighbors decrease. There is little doubt that strong starbursts happen in the nuclei of VLIRGs. Assuming class 0 as advanced merger, we construct a simple merger sequence, from morphological classes 1 to 4 (with near or far companions), to class 5 and 6 (interacting pairs and mergers) and then to class 0 (isolated galaxies). Along this sequence, VLIRGs evolve from HII galaxies to AGNs.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A89
- Title:
- Very metal poor stars in MW halo
- Short Name:
- J/A+A/608/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of 59 very metal-poor (VMP, -4<=[Fe/H]<~-2) stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW) halo. Our results are based on high-resolution spectroscopic datasets and homogeneous and accurate atmospheric parameters determined in Paper I. We show that once the NLTE effects are properly taken into account, all massive galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [alpha/Fe]=0.3 for each of the alpha-process elements: Mg, Ca, and Ti. We put on a firm ground the evidence for a decline in alpha/Fe with increasing metallicity in the Bootes I ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs reveal indistinguishable trends with metallicity, suggesting that the processes of Na and Al synthesis are identical in all systems, independent of their mass. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. We show that Sr in the massive galaxies is better correlated with Mg than Fe and that its origin is essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs, that is Bootes I, UMa II, and Leo IV, are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg]=-1.3 and [Ba/Mg]=-1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Bootes I and UMa II indicate a common r-process origin of their neutron-capture elements. Sculptor remains the classical dSph, in which the evidence for inhomogeneous mixing in the early evolution stage, at [Fe/H]<-2, is the strongest.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/3784
- Title:
- Very thin discs galaxies properties
- Short Name:
- J/MNRAS/465/3784
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the properties of galaxies with very thin discs (VTDs) using a sample of 85 objects whose stellar disc radial-to-vertical scale ratio determined from photometric decomposition, exceeds 9. We present evidences of similarities between the VTD galaxies and low surface brightness (LSB) disc galaxies, and conclude that both small and giant LSB galaxies may reveal themselves as VTD, edge-on galaxies. Our VTD galaxies are mostly bulgeless, and those with large radial scalelength tend to have redder colours. We performed spectral observations of 22 VTD galaxies with the Dual Imaging Spectrograph on the 3.5 m telescope at the Apache Point Observatory. The spectra with good resolution (R~5000) allow us to determine the distance and the ionized gas rotation curve maximum for the galaxies. Our VTD galaxies have low dust content, in contrast to regular disc galaxies. Apparently, VTD galaxies reside in specific cosmological low-density environments and tend to have less connection with filaments. Comparing a toy model that assumes marginally low star formation in galactic discs with obtained gas kinematics data, we conclude that there is a threshold central surface density of about 88M_{sun}_/pc^2^, which we observe in the case of very thin, rotationally supported galactic discs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/492/1791
- Title:
- Very young galaxies from SDSS
- Short Name:
- J/MNRAS/492/1791
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Only a handful of galaxies in the local Universe appear to be very young. We estimate the fraction of very young galaxies (VYGs), defined as those with more than half their stellar masses formed within the last Gyr. We fit non-parametric star formation histories (SFHs) to ~280000 galaxy spectra from a flux- and volume-limited subsample of the Main Galaxy Sample (MGS) of the SDSS, which is also complete in mass-to-light ratio, thus properly accounting for passive galaxies of a given mass. The VYG fractions decrease with increasing galaxy stellar mass, from ~50 per cent at m=10^8^M_{sun}_ to ~0.1 per cent at m=10^11.5^M_{sun}_, with differences of up to 1dex between the different spectral models used to estimate the SFH and on how we treat aperture effects. But old stellar populations may hide in our VYGs despite our conservative VYG sample built with galaxies that are globally bluer than within the region viewed by the SDSS fibre. The VYG fractions versus mass decrease more gradually compared to the Tweed et al. (2018MNRAS.477.1427T) predictions using analytical and semi-analytical models of galaxy formation, but agree better with the SIMBA hydrodynamical simulation. These discrepancies highlight the usefulness of VYGs in constraining the strong uncertainties in both galaxy formation models and spectral modelling of galaxy SFHs. Given the lognormal cosmic SFH, these mean VYG fractions suggest that galaxies above 10^8^M_{sun}_ undergo at most four major starbursts on average.
