- ID:
- ivo://CDS.VizieR/J/ApJ/897/183
- Title:
- Chemical abundances of 3 stars in Grus II galaxy
- Short Name:
- J/ApJ/897/183
- Date:
- 15 Mar 2022 04:18:06
- Publisher:
- CDS
- Description:
- We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy GrusII. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass (>=20M{sun}) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of GrusII could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high- mass stars, thus the possible top-heavy initial mass function of GrusII would increase the likelihood of any of these events occurring. The time delay between the {alpha} and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in GrusII.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/599/A97
- Title:
- Chemical composition of globular cluster NGC 6426
- Short Name:
- J/A+A/599/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widths and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H]=-2.34+/-0.05dex (stat.) in accordance with previous studies. At a mean {alpha}-abundance of [(Mg,Si,Ca)/3Fe]=0.39+/-0.03dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter {alpha}-elements as well as the enhanced ratio [Zn/Fe]=0.39dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn point towards an enrichment history governed by the r-process with only little - if any - sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A176
- Title:
- Chemical evolution of dSph galaxy Sextans
- Short Name:
- J/A+A/642/A176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our analysis of the FLAMES dataset targeting the central 25' region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team (DART). Our sample is composed of red giant branch stars down to V~20.5mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H]=-3.2 to -1.5dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in [alpha/Fe] at ~0.4dex followed by a decrease above [Fe/H]~-2dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H]~-2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A10
- Title:
- Chemo-kinematic properties of Aquarius
- Short Name:
- J/A+A/634/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to have interacted with the large LG spirals, and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution. We aim to provide insight into the internal mechanisms shaping LG dwarf galaxies by increasing our knowledge of the internal properties of isolated systems. Here we focus on the evolved stellar component of the Aquarius dwarf galaxy, whose kinematic and metallicity properties have only recently started to be explored. Spectroscopic data in the region of the near-infrared Ca~II triplet lines has been obtained with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars. These data are used to derive line-of-sight velocities and [Fe/H] of the individual RGB stars. We have derived a systemic velocity of -142.2^+1.8^_-1.8_km/s, in agreement with previous determinations from both the HI gas and stars. The internal kinematics of Aquarius appears to be best modelled by a combination of random motions (l.o.s. velocity dispersion of 10.3^+1.6^_-1.3_km/s) and linear rotation (with a gradient -5.0^+1.6^_-1.9_km/s/arcmin) along a P.A.=139_-27_^+17^deg, broadly consistent with the optical projected major axis. This rotation signal is significantly misaligned or even counter-rotating to that derived from the HI gas. We also find the tentative presence of a mild negative metallicity gradient and indications that the metal-rich stars have a colder velocity dispersion than the metal-poor ones. This work represents a significant improvement with respect to previous measurements of the RGB stars of Aquarius, as it doubles the number of member stars already studied in the literature. We speculate that the misaligned rotation between the HI gas and evolved stellar component might have been the result of recent accretion of HI gas, or re-accretion after gas-loss due to internal stellar feedback.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A6
- Title:
- 3C293 high and low resolution maps
- Short Name:
- J/A+A/658/A6
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Active galactic nuclei (AGNs) show episodic activity, which can be evident in galaxies that exhibit restarted radio jets. These restarted jets can interact with their environment, leaving signatures on the radio spectral energy distribution. Tracing these signatures is a powerful way to explore the life of radio galaxies. This requires resolved spectral index measurements over a broad frequency range including low frequencies. We present such a study for the radio galaxy 3C293, which has long been thought to be a restarted galaxy on the basis of its radio morphology. Using the International LOFAR telescope (ILT) we probed spatial scales as fine as ~0.2-arcsec at 144MHz, and to constrain the spectrum we combined these data with Multi-Element Radio Linked Interferometer Network (MERLIN) and Very Large Array (VLA) archival data at frequencies up to 8.4GHz that have a comparable resolution. In the inner lobes (~2kpc), we detect the presence of a spectral turnover that peaks at ~225MHz and is most likely caused by free-free absorption from the rich surrounding medium. We confirm that these inner lobes are part of a jet-dominated young radio source (spectral age ~0.17Myr), which is strongly interacting with the rich int <0.27Myr. The outer lobes (extending up to ~100kpc) have a spectral index of ~0.6-0.8 from 144-4850MHz with a remarkably uniform spatial distribution and only mild spectral curvature. We propose that intermittent fuelling and jet flow disruptions are powering the mechanisms that keep the spectral index in the outer lobes from steepening and maintain the spatial uniformity of the spectral index. Overall, it appears that 3C293 has gone through multiple (two to three) epochs of activity. This study adds 3C293 to the new sub-group of restarted galaxies with short interruption time periods. This is the first time a spatially resolved study has been performed that simultaneously studies a young source as well as the older outer lobes at such low frequencies. This illustrates the potential of the International LOFAR telescope to expand such studies to a larger sample of radio galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A122
- Title:
- 3C 273 high energy spectrum
- Short Name:
- J/A+A/576/A122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The high energy spectrum of 3C 273 is usually understood in terms of inverse-Compton emission in a relativistic leptonic jet. This model predicts variability patterns and delays that could be tested with simultaneous observations from the radio to the GeV range. The instruments IBIS, SPI, JEM-X on board INTEGRAL, PCA on board RXTE, and LAT on board Fermi have enough sensitivity to follow the spectral variability of 3C 273 from the keV to the GeV. We looked for correlations between the different energy bands, including radio data at 37GHz collected at the Metsahovi Radio Observatory and built quasi-simultaneous multiwavelength spectra in the high energy domain when the source is flaring either in the X-rays or in the {gamma} rays.
- ID:
- ivo://CDS.VizieR/J/MNRAS/433/543
- Title:
- Choirs, HI galaxy groups
- Short Name:
- J/MNRAS/433/543
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- H{alpha} observations centred on galaxies selected from the Hi Parkes All-Sky Survey (HiPASS) typically show one and sometimes two star-forming galaxies within the ~15arcmin beam of the Parkes 64m HI detections. In our Survey for Ionization in Neutral Gas Galaxies (SINGG) we found 15 cases of HiPASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case, we found a field with at least nine ELGs. In this paper, we present a catalogue of Choir group members in the context of the wider SINGG sample. The dwarf galaxies in the Choir groups would not be individually detectable in HiPASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total HI mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, H{alpha} equivalent width and surface brightness. Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly Hi deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (SFE; the ratio of star formation rate to HI mass), showing an increasing trend in SFE with stellar mass.
- ID:
- ivo://CDS.VizieR/J/A+A/563/L6
- Title:
- CIG 638 CCH, HCN. HOC and HNC spectra
- Short Name:
- J/A+A/563/L6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multi-molecule observations towards an increasing variety of galaxies have been showing that the relative molecular abundances are affected by the type of activity. However, these studies are biased towards bright active galaxies, which are typically in interaction. We study the molecular composition of one of the most isolated galaxies in the local Universe where the physical and chemical properties of their molecular clouds have been determined by intrinsic mechanisms.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A163
- Title:
- CIG 96 deep optical and HI images
- Short Name:
- J/A+A/619/A163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Asymmetries in atomic hydrogen (HI) in galaxies are often caused by the interaction with close companions, making isolated galaxies an ideal framework to study secular evolution. The AMIGA project has demonstrated that isolated galaxies show the lowest level of asymmetry in their HI integrated profiles compared to even field galaxies, yet some present significant asymmetries. CIG 96 (NGC 864) is a representative case reaching a 16% level. Our aim is to investigate the HI asymmetries of the spiral galaxy CIG 96 and what processes have triggered the star-forming regions observed in the XUV pseudo-ring. We performed deep optical observations at CAHA1.23m, CAHA2.2m and VST (OmegaCAM wide-field camera) telescopes. We reach surface brightness (SB) limits of {mu}_CAHA2.2m_=27.5mag/arcsec^2^ (Cousins R) and {mu}_VST_=28.7mag/arcsec^2^ (SDSS r) that show the XUV pseudo-ring of the galaxy in detail. Additionally, a wavelet filtering of the HI data cube from our deep observations with VLA/EVLA telescope allowed us to reach a column density of N_HI_=8.9x10^18^cm^-2^ (5{sigma}) (28"x28" beam), lower than in any isolated galaxy. We confirm that the HI of CIG 96 extends farther than 4xr_25_ in all directions. Furthermore, we detect for the first time two gaseous structures (~10^6^M_{sun}_) in the outskirts. The SDSS g-r colour index image from CAHA1.23m shows extremely blue colours in certain regions of the pseudo-ring where N_HI_>8.5x10^20^cm^-2^, whereas the rest show red colours. Galactic cirrus contaminate the field, setting an unavoidable detection limit at 28.5mag/arcsec^2^ (SDSS r). At the current SB and NHI levels, we detect no stellar link within 1{deg}x1{deg} or gaseous link within 40'x40' between CIG 96 and any companion. The isolation criteria rule out interactions with other similar-sized galaxies for at least 2.7Gyr. Using existing stellar evolution models, the age of the pseudo-ring is estimated at 1Gyr or older. Undetected previously accreted companions and cold gas accretion remain as the main hypothesis to explain the optical pseudo-ring and HI features of CIG 96.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A56
- Title:
- CIG 340 (IC 2487) HI mapping
- Short Name:
- J/A+A/567/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HI kinematic asymmetries are common in late-type galaxies irrespective of environment, although the amplitudes are strikingly low in isolated galaxies. As part of our studies of the HI morphology and kinematics in isolated late-type galaxies we have chosen several very isolated galaxies from the AMIGA sample for HI mapping. We present here the results of HI mapping of CIG 340 (IC 2487) which was selected because its integrated HI spectrum has a very symmetric profile (A_flux_=1.03+/-0.02). Optical images of the galaxy hinted at a warped disk in contrast to the symmetric integrated HI spectrum profile. Our aim is to determine the extent to which the optical asymmetry is reflected in the resolved HI morphology and kinematics. Resolved 21-cm HI line mapping has been carried out using the Giant Metrewave Radio Telescope (GMRT). The HI morphology and kinematics from this mapping together with other multi-wavelength data have been used to study the relationship between the HI and stellar components of CIG 340.