High Metallicity Systems Research Articles

Stellar populations and merger rates of brightest cluster galaxies a billion years ago: SDSS MaNGA IFU spectroscopy

ABSTRACT We investigate the spectroscopic properties of 85 brightest cluster galaxies (BCGs) and their companions observed with the SDSS MaNGA integral field unit. Galaxy redshifts are between 0.08 < z < 0.15, allowing for a field-of-view up to 80 × 80 kpc. For the main galaxies: the average age of the BCG cores is 7.66$\, \pm \,$1.36 Gyr with no significant gradient out to $2\, R_ {e}$; the average metallicity of the BCG cores is $[Z/H]=0.23\, \pm \, 0.03$ with a negative gradient of Δ[Z/H]/Δ(R/Re) = –0.14$\, \pm \, 0.09$ which flattens beyond $1.2\, R_ {e}$. Velocity dispersion gradients are mostly flat, but a few positive slopes are seen in the most massive galaxies. Emission lines are present in 12 of the BCGs, most often confined to the central $\sim 2\,$ kpc with emission line ratios well-described by a LINER or AGN excitation source. There are 78 companion galaxies identified and 9 have nebular emission lines that indicate recent star formation. The companions with flux ratios of 4:1 and 20:1 within 30 kpc of their BCG’s core are studied. The companion galaxies have a median age of 7.65$\, \pm \,$1.55 Gyr and are high-metallicity systems, with a median [Z/H] = 0.17 ± 0.07. Close spectroscopic companions with higher merging probabilities have an average merging time of 0.5 ± 0.2 Gyr. The average merger rate is 0.08$\, \pm \, 0.12 \,$ Gyr−1 for 4:1 companions and 0.26$\, \pm \, 0.22 \,$ Gyr−1 for 20:1 companions, allowing for an increase in mass of 2.3$\, \pm \,$3.4 per cent Gyr−1 and 3.5$\, \pm \,$3.2 per cent Gyr−1, respectively.

H2 molecular gas absorption-selected systems trace CO molecular gas-rich galaxy overdensities

ABSTRACT Absorption-selected galaxies offer an effective way to study low-mass galaxies at high redshift. However, the physical properties of the underlying galaxy population remain uncertain. In particular, the multiphase circumgalactic medium is thought to hold key information on gas flows into and out of galaxies that are vital for galaxy evolution models. Here, we present ALMA observations of CO molecular gas in host galaxies of H2-bearing absorbers. In our sample of six absorbers, we detect molecular gas-rich galaxies in five absorber fields, although we did not target high-metallicity (>50 per cent solar) systems for which previous studies reported the highest detection rate. Surprisingly, we find that the majority of the absorbers are associated with multiple galaxies rather than single haloes. Together with the large impact parameters, these results suggest that the H2-bearing gas seen in absorption is not part of an extended disc, but resides in dense gas pockets in the circumgalactic and intragroup medium.

A diffuse tidal dwarf galaxy destined to fade out as a “dark galaxy”

We have explored the properties of a peculiar object detected in deep optical imaging and located at the tip of an H I tail emerging from Hickson Compact Group 16. Using multiband photometry from infrared to ultraviolet, we were able to constrain its stellar age to 58−9+22 Myr with a rather high metallicity of [Fe/H] = −0.16−0.41+0.43 for its stellar mass of M⋆ = 4.2 × 106 M⊙, a typical signature of tidal dwarf galaxies. The structural properties of this object are similar to those of diffuse galaxies, with a round and featureless morphology, a large effective radius (reff = 1.5 kpc), and a low surface brightness (⟨μg⟩eff = 25.6 mag arcsec−2). Assuming that the object is dynamically stable and able to survive in the future, its fading in time via the aging of its stellar component will make it undetectable in optical observations in just ∼2 Gyr of evolution, even in the deepest current or future optical surveys. Its high H I mass, M(HI) = 3.9 × 108 M⊙, and future undetectable stellar component will make the object match the observational properties of dark galaxies, that is, dark matter halos that failed to turn gas into stars. Our work presents further observational evidence of the feasibility of H I tidal features becoming fake dark galaxies; it also shows the impact of stellar fading, particularly in high metallicity systems such as tidal dwarfs, in hiding aged stellar components beyond detection limits in optical observations.

Neutral-gas-phase metal abundances in Zn ii-selected quasar absorption line systems near redshift z = 1.2★

We present ten metallicity measurements for quasar absorbers near $z=1.2$ that were selected for having unusually significant ZnII absorption in their SDSS spectra. Follow-up UV space spectroscopy of the Ly$\alpha$ region shows that all ten have damped Ly$\alpha$ (DLA) absorption, corresponding to neutral hydrogen column densities in the range $2.4\times 10^{20}$ $\le$ N(HI) $\le$ $2.5\times 10^{21}$ atoms cm$^{-2}$, and indicating that the gas is very optically thick and essentially neutral. The sample is a very small subset of systems compiled by searching the University of Pittsburgh catalog of $\approx 30,000$ intervening MgII absorption line systems in SDSS quasar spectra up to DR7. We started by isolating $\approx 3,000$ that had strong MgII absorption in the redshift interval $1.0 < z < 1.5$ in brighter background quasars. Of these, 36 exhibited significant absorption near ZnII. Space UV spectroscopy was then obtained for nine of these (25% of the total), and a tenth system in a fainter quasar was found in the HST archives. The result is a representative sample of the highest Zn$^+$ columns of gas within the DLA population. These ZnII-selected systems define the upper envelope of DLA metallicities near $z=1.2$. They show a tight anti-correlation between N(HI) and [Zn/H], with the higher metallicity systems clearly exhibiting more depletion based on [Cr/Zn] values. The various metal-line measurements (Zn, Cr, Si, Fe, Mn) indicate evolved neutral gas with $-0.9 \le$ [Zn/H] $\le +0.4$.

Jupiter Analogs Orbit Stars with an Average Metallicity Close to That of the Sun

Abstract Jupiter played an important role in determining the structure and configuration of the Solar System. Whereas hot-Jupiter type exoplanets preferentially form around metal-rich stars, the conditions required for the formation of planets with masses, orbits, and eccentricities comparable to Jupiter (Jupiter analogs) are unknown. Using spectroscopic metallicities, we show that stars hosting Jupiter analogs have an average metallicity close to solar, in contrast to their hot-Jupiter and eccentric cool-Jupiter counterparts, which orbit stars with super-solar metallicities. Furthermore, the eccentricities of Jupiter analogs increase with host-star metallicity, suggesting that planet–planet scatterings producing highly eccentric cool Jupiters could be more common in metal-rich environments. To investigate a possible explanation for these metallicity trends, we compare the observations to numerical simulations, which indicate that metal-rich stars typically form multiple Jupiters, leading to planet–planet interactions and, hence, a prevalence of either eccentric cool Jupiters or hot Jupiters with circularized orbits. Although the samples are small and exhibit variations in their metallicities, suggesting that numerous processes other than metallicity affect the formation of planetary systems, the data in hand suggests that Jupiter analogs and terrestrial-sized planets form around stars with average metallicities close to solar, whereas high-metallicity systems preferentially host eccentric cool Jupiter or hot Jupiters, indicating that higher metallicity systems may not be favorable for the formation of planetary systems akin to the Solar System.

Torques Induced by Scattered Pebble-flow in Protoplanetary Disks

Abstract Fast inward migration of planetary cores is a common problem in the current planet formation paradigm. Even though dust is ubiquitous in protoplanetary disks, its dynamical role in the migration history of planetary embryos has not been assessed. In this Letter, we show that the scattered pebble-flow induced by a low-mass planetary embryo leads to an asymmetric dust-density distribution that is able to exert a net torque. By analyzing a large suite of multifluid hydrodynamical simulations addressing the interaction between the disk and a low-mass planet on a fixed circular orbit, and neglecting dust feedback onto the gas, we identify two different regimes, gas- and gravity-dominated, where the scattered pebble-flow results in almost all cases in positive torques. We collect our measurements in a first torque map for dusty disks, which will enable the incorporation of the effect of dust dynamics on migration into population synthesis models. Depending on the dust drift speed, the dust-to-gas mass ratio/distribution, and the embryo mass, the dust-induced torque has the potential to halt inward migration or even induce fast outward migration of planetary cores. We thus anticipate that dust-driven migration could play a dominant role during the formation history of planets. Because dust torques scale with disk metallicity, we propose that dust-driven outward migration may enhance the occurrence of distant giant planets in higher-metallicity systems.

YOUNG STARS AND IONIZED NEBULAE IN M83: COMPARING CHEMICAL ABUNDANCES AT HIGH METALLICITY

ABSTRACT We present spectra of 14 A-type supergiants in the metal-rich spiral galaxy M83. We derive stellar parameters and metallicities and measure a spectroscopic distance modulus (4.9 ± 0.2 Mpc), in agreement with other methods. We use the stellar characteristic metallicity of M83 and other systems to discuss a version of the galaxy mass–metallicity relation that is independent of the analysis of nebular emission lines and the associated systematic uncertainties. We reproduce the radial metallicity gradient of M83, which flattens at large radii, with a chemical evolution model, constraining gas inflow and outflow processes. We carry out a comparative analysis of the metallicities we derive from the stellar spectra and published H ii region line fluxes, utilizing both the direct, -based method and different strong-line abundance diagnostics. The direct abundances are in relatively good agreement with the stellar metallicities, once we apply a modest correction to the nebular oxygen abundance due to depletion onto dust. Popular empirically calibrated strong-line diagnostics tend to provide nebular abundances that underestimate the stellar metallicities above the solar value by ∼0.2 dex. This result could be related to difficulties in selecting calibration samples at high metallicity. The O3N2 method calibrated by Pettini and Pagel gives the best agreement with our stellar metallicities. We confirm that metal recombination lines yield nebular abundances that agree with the stellar abundances for high-metallicity systems, but find evidence that in more metal-poor environments they tend to underestimate the stellar metallicities by a significant amount, opposite to the behavior of the direct method.

ON THE ABSENCE OF HIGH METALLICITY-HIGH COLUMN DENSITY DAMPED Lyα SYSTEMS: MOLECULE FORMATION IN A TWO-PHASE INTERSTELLAR MEDIUM

We argue that the lack of observed damped Lyα (DLA) systems that simultaneously have high H i column densities and high metallicities results naturally from the formation of molecules in the cold phase of a two-phase atomic medium in pressure balance. Our result applies equally well in diffuse systems where the ultraviolet radiation field is dominated by the extragalactic background and in dense star-forming ones, where the local radiation field is likely to be orders of magnitude higher. We point out that such a radiation-insensitive model is required to explain the absence of high column–high metallicity systems among DLAs observed using gamma-ray burst (GRB) afterglows, since these are likely subjected to strong radiation fields created by active star formation in the GRB host galaxy. Moreover, we show that the observed relationship between the maximum atomic gas column in DLAs sets a firm upper limit on the fraction of the mass in these systems that can be in the warm, diffuse phase. Finally, we argue that our result explains the observed lack of in situ star formation in DLA systems.

MODELING THE RETENTION PROBABILITY OF BLACK HOLES IN GLOBULAR CLUSTERS: KICKS AND RATES

We simulate black hole binary interactions to examine the probability of mergers and black hole growth and gravitational radiation signals using a specific initial distribution of masses for black holes in globular clusters and a simple semi-analytic formalism for dynamical interactions. We include 3-body recoil and the latest results in numerical relativity for gravitational radiation recoil. It is found that while 99% of binaries are ejected from low metallicity, low mass clusters; metal rich massive clusters retain 5% of their binaries. An interesting fraction of the ejected binaries, especially those from high mass, high metallicity systems, merge on timescales short enough to be gravitational radiation sources during their mergers with rates approaching those expected for galactic field black hole binaries. While the merger rates are comparable, the much larger mass of these binaries and their localization will make them appealing targets for advanced LIGO. We single out two possible Milky Way clusters (NGC 6441 and NGC 6388) as having the properties for a good probability of retention.

Expected planets in globular clusters

We argue that all transient searches for planets in globular clusters have a very low detection probability. Planets of low-metallicity stars typically do not reside at small orbital separations. The dependence of planetary system properties on metallicity is clearly seen when the quantity Ie ≡ Mp[a(1 − e)] 2 is considered; Mp, a and e are the planet mass, semimajor axis and eccentricity, respectively. In high-metallicity systems, there is a concentration of systems at high and low values of Ie, with a low-populated gap near Ie ∼ 0.3MJ au 2 , where MJ is Jupiter’s mass. In low-metallicity systems, the concentration is only at the higher range of Ie, with a tail to low values of Ie. Therefore, it is still possible that planets exist around main-sequence stars in globular clusters, although at small numbers because of the low metallicity, and at orbital periods of � 10 d. We discuss the implications of our conclusions on the role that companions can play in the evolution of their parent stars in globular clusters, for example, influencing the distribution of horizontal branch stars on the Hertzsprung‐Russell diagram of some globular clusters, and in forming low-mass white dwarfs.

A mid-infrared spectroscopic survey of starburst galaxies: Excitation and abundances

We present spectroscopy of MIR emission lines in twelve starburst regions, located in eleven starburst galaxies, for which a significant number of lines between 2.38 and 45micron were observed with the ISO Short Wavelength Spectrometer, with the intention of providing a reference resource for MIR spectra of starburst galaxies. The observation apertures were centred on actively star forming regions, including those which are inaccessible at optical wavelengths due to high levels of obscuration. We use this data set, which includes fine structure and hydrogen recombination lines, to investigate excitation and to derive gas phase abundances of neon, argon, and sulphur of the starburst galaxies. The derived Ne abundances span approximately an order of magnitude, up to values of ~3 times solar. The excitation ratios measured from the Ne and Ar lines correlate well with each other (positively) and with abundances (negatively). Both in excitation and abundance, a separation of objects with visible Wolf-Rayet features (high excitation, low abundance) is noted from those without (low excitation, high abundance). For a given abundance, the starbursts are of relatively lower excitation than a comparative sample of HII regions, possibly due to ageing stellar populations. By considering the abundance ratios of S with Ne and Ar we find that, in our higher metallicity systems, S is relatively underabundant by a factor of ~3. We discuss the origin of this deficit and favour depletion of S onto dust grains as a likely explanation. This weakness of the MIR fine structure lines of S has ramifications for future infrared missions such as SIRTF and Herschel since it indicates that the S lines are less favourable tracers of star formation than is suggested by nebular models which do not consider this effect.

Metallicity in damped Lyman- systems: evolution or bias?

Assuming that damped Lyman-alpha(DLA) systems are galactic discs, we calculate the corresponding evolution of metal abundances. We use detailed multi-zone models of galactic chemical evolution (reproducing successfully the observed properties of disc galaxies) and appropriate statistics (including geometrical propability factors) to calculate the average metallicity as a function of redshift. The results are compatible with available observations, provided that observational biases are taken into account, as suggested by Boisse et al. (1998). In particular, high column density and high metallicity systems are not detected because the light of backround quasars is severely extinguished, while low column density and low metallicity systems are not detectable through their absorption lines by current surveys. We show that these observational constraints lead to a ``no-evolution'' picture for the DLA metallicity, which does not allow to draw strong conclusions about the nature of those systems or about their role in ``cosmic chemical evolution''.

Photodissociation Regions in the Large Magellanic Cloud and IC 10

Both theory and observation suggest that metallicity profoundly alters the properties and structure of the Photodissociation Regions (PDRs; e.g., Madden et al. 1997). Several factors contribute to the differences between high and low metallicity systems: altered gas phase and grain surface chemistry due to the low Si, C and S elemental abundances, and diminished dust shielding because of the low dust-to-gas ratio. Since there is less dust shielding, UV photons penetrate more deeply into the molecular clouds leaving H2 unaffected but photodissociating most other molecules everywhere except in the most opaque clumps. Thus, a low-metallicity system contains large regions where hydrogen remains molecular but the usual tracers of molecular gas like CO are photodissociated.

What the galaxies of the Local Group tell us about massive star evolution

We consider what we've learned about massive star evolution from observations of the resolved stellar content of Local Group galaxies. Studies of mixed-age (galaxy-wide) and coeval (single associations) populations reveal much about massive star evolution, and how it is controlled by metallicity, demonstrating the ‘Conti scenario’ in action! The number of WC stars to WN stars increases with increasing metallicity, as expected: in regions of higher metallicity stars of somewhat lower luminosity can evolve all the way to the WC stage. The exception is the starburst galaxy IC 10, for which I speculate that the IMF may be weighted towards high mass stars. The highest luminosity red supergiants are lacking in galaxies of higher metallicity, suggesting that the stars that would have become these RSGs are spending more of their time as WRs. The presence of luminous RSGs is highly correlated with the presence of WC and WN stars in OB associations, suggesting that many massive stars evolve through both a RSG and WR stage. The relative number of RSGs and WRs does decrease strongly with increasing metallicity, again consistent with higher metallicity systems leading to increased time in the WR phase. The various WC subclasses appear to be the result of the influence of metallicity on stellar wind structure in these stars, and are not due to to differences in mass or luminosity. Data on the field population in the Magellanic Clouds suggest that stars more massive than 30 become WRs in the LMC, while the limit may be more like 50 in the SMC, again as expected. Studies of the turn-off masses in clusters and associations in the MCs and Milky Way are nearing completion, while investigations in the more distant galaxies of the Local Group are just getting underway. For the LMC we find the following: WNE stars come from a large mass range of progenitor (30–100 ), and have very large (negative) bolometric corrections (−6 to −8 mag). The Ofpe/WN9 stars seem to come from lower mass progenitor (20–30 ), and have more modest BCs (−1 to −3 mag). WC stars come from stars with masses &gt; 60–70 , and have BCs of −3 to −4 mag. Both ‘B2I+WN3’ systems and LBV stars like S Doradus are found only in clusters containing very high turn off masses (&gt;70–90 ).

Evolved Massive Stars in the Local Group. I. Identification of Red Supergiants in NGC 6822, M31, and M33

Knowledge of the red supergiant (RSG) population of nearby galaxies allows us to probe massive star evolution as a function of metallicity; however, contamination by foreground Galactic dwarfs dominates surveys for red stars in Local Group galaxies beyond the Magellanic Clouds. Model atmospheres predict that low-gravity supergiants will have B-V values that are redder by several tenths of a magnitude than foreground dwarfs at a given V-R color, a result that is largely independent of reddening. We conduct a BVR survey of several fields in the Local Group galaxies NGC 6822, M33, and M31 as well as neighboring control fields and identify RSG candidates from CCD photometry. The survey is complete to V = 20.5, corresponding to MV = -4.5 or an Mbol of -6.3 for the reddest stars. Follow-up spectroscopy at the Ca II triplet of 130 stars is used to demonstrate that our photometric criterion for identifying RSGs is highly successful (96% for stars brighter than V = 19.5; 82% for V = 19.5-20.5). Classification spectra are also obtained for a number of stars in order to calibrate color with spectral type empirically. We find that there is a marked progression in the average (B-V)0 and (V-R)0 colors of RSGs in these three galaxies, with the higher metallicity systems having a later average spectral type, which is consistent with previous findings by Elias, Frogel, & Humphreys for the Milky Way and Magellanic Clouds. More significantly, we find that there is a clear progression with metallicity in the relative number of the highest luminosity RSGs, a trend that is apparent both in absolute visual magnitude and in bolometric luminosity. Thus any use of RSGs as distance indicators requires correction for the metallicity of the parent galaxy. Our findings are in accord with the predictions of the Conti scenario in which higher metallicities result in higher mass-loss rates, resulting in a star of a given luminosity spending an increasing fraction of its He-burning lifetime as a Wolf-Rayet (WR) star rather than as an RSG with increasing metallicity. The fact that the distribution of luminosities have extended tails extending to higher luminosity (with the possible exception of the M31 sample, which contains only one high-luminosity RSG) suggests that many WRs may pass through an RSG phase, albeit for a short period. We find that over the factor of 5 difference in metallicity from NGC 6822 to M31, the masses of the most luminous RSGs change by about a factor of 2, with the highest mass RSGs having masses of 25-30 M☉ in NGC 6822, 18 M☉ in M33, and 13-15 M☉ in M31. These masses are lower than the usually assumed limits for evolution to the WR stage but are not necessarily in conflict with the number of unevolved O and B stars if the time spent as a He-burning object is split between the RSG and WR phases over a large mass range.

Consequences of Dust in Metal-rich H II Regions

view Abstract Citations (91) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Consequences of Dust in Metal-rich H II Regions Shields, Joseph C. ; Kennicutt, Robert C., Jr. Abstract Dust and associated depletion of heavy elements from the gas phase can modify the thermal properties of H II regions from the dust-free case, with significant consequences for the emergent optical spectrum. We present the results of theoretical calculations illustrating the effects of grains on the spectra of giant, extragalactic H II regions, with emphasis on high-metallicity systems (Z ≳ Zsun). Dust provides a simple explanation for the observational absence of pure Balmer line spectra that are expected on theoretical grounds for dust- free, chemically enriched nebulae. Grains may also play a role in enhancements of forbidden-line emission observed in H II regions in the enriched nuclei of normal galaxies. In most cases, depletion introduces the strongest perturbations to the optical spectrum. Selective absorption of the ionizing continuum as well as heating by grain photoelectrons are important in some instances, however, and grain heating can be particularly important for enhancing emission in high-ionization lines. Allowing for depletion, the presence of dust is unlikely to introduce large errors in global metallicity indicators, although uncertainties in depletion factors coupled with the sensitivity of infrared cooling to electron density will make accurate calibrations difficult at high Z. The present calculations establish further that previous relative abundance analyses that fail to take into account dust effects in a self-consistent way (grain heating as well as depletion) may overestimate temperature gradients in high-Z nebulae, resulting in errors in relative abundances for different elements. Publication: The Astrophysical Journal Pub Date: December 1995 DOI: 10.1086/176533 arXiv: arXiv:astro-ph/9509137 Bibcode: 1995ApJ...454..807S Keywords: ISM: DUST; EXTINCTION; ISM: H II REGIONS; ISM: ABUNDANCES; Astrophysics E-Print: 21 pages (AASTeX), plus 9 figures (uuencoded, gzipped, tar), to appear in ApJ, December 1995 full text sources arXiv | ADS |

Element abundances in H II galaxies

view Abstract Citations (119) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Element Abundances in H II Galaxies Masegosa, Josefa ; Moles, Mariano ; Campos-Aguilar, Ana Abstract Data for 121 H II systems from the spectrophotometric catalog of H II galaxies (Terlevich et al. 1991) have been analyzed to determine the abundances of the most common chemical elements. The range of O/H spanned by the data is from 0.5 to 0.03 the solar value. The rarity of objects in the sample with metallicities similar to that of I Zw 18 could correspond to the claimed increasing probability to find low-metallicity objects among intrinsically fainter systems. It is argued that the correction for ionization for Ne could be inadequate due to the transformation of part of the O^++^ into O^+^ in the high-ionization zone through charge transfer reactions. The apparent overabundance of Ne found in low-excitation objects would then be just an artifact. When the analysis is restricted to high-excitation nebulae (O^++^/O > 0.9), we find a constant Ne/O = 0.17 ratio, in agreement with the current ideas about the nucleosynthesis of those two elements. The N/O ratio, once the systems with detected traces of the presence of shocks were discarded, was found to be constant at the level 0.032. Thus, for those objects, N is essentially primary in origin. On the other hand, the greater N abundances in higher metallicity systems would indicate that secondary production is at work in them. Those mechanisms, however, are operative only when the metallicity is greater than some threshold value. The last element we have considered is helium. It is argued that none of the proposed ionization correction schemes works correctly, so only objects for which the amount of neutral He is seemingly negligible can be retained to determine He abundances. It is remarked that the selection by effective temperature corresponds in fact to a selection by metallicity. The lower envelope of the He abundances we find is about 22%. We do not find any trend between the He content and the abundances of other elements like O or N. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173588 Bibcode: 1994ApJ...420..576M Keywords: Abundance; H Ii Regions; Ionization; Nebulae; Star Formation; Astronomical Catalogs; Charge Transfer; Helium; Metallicity; Neon; Nitrogen; Nuclear Fusion; Oxygen; Astrophysics; GALAXIES: ABUNDANCES; ISM: H II REGIONS full text sources ADS | data products SIMBAD (79) NED (74)