CHAOS. III. GAS-PHASE ABUNDANCES IN NGC 5457 Croxall, Kevin V.; Pogge, Richard W.; Berg, Danielle A. ...
Astrophysical journal/The Astrophysical journal,
10/2016, Letnik:
830, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We present Large Binocular Telescope observations of 109 H ii regions in NGC 5457 (M101) obtained with the Multi-Object Double Spectrograph. We have robust measurements of one or more ...temperature-sensitive auroral emission lines for 74 H ii regions, permitting the measurement of "direct" gas-phase abundances. Comparing the temperatures derived from the different ionic species, we find: (1) strong correlations of TN ii with TS iii and TO iii, consistent with little or no intrinsic scatter; (2) a correlation of TS iii with TO iii, but with significant intrinsic dispersion; (3) overall agreement between TN ii, TS ii, and TO ii, as expected, but with significant outliers; (4) the correlations of TN ii with TS iii and TO iii match the predictions of photoionization modeling while the correlation of TS iii with TO iii is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation H ii regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of H ii regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074 0.009 in O/H and 0.095 0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct abundance measurements of H ii regions in NGC 5457.
ABSTRACT The CHemical Abundances of Spirals (CHAOS) project leverages the combined power of the Large Binocular Telescope (LBT) with the broad spectral range and sensitivity of the Multi Object ...Double Spectrograph (MODS) to measure "direct" abundances (based on observations of the temperature-sensitive auroral lines) in large samples of H ii regions in spiral galaxies. We present LBT MODS observations of 62 H ii regions in the nearby spiral galaxy NGC 628, with an unprecedentedly large number of auroral lines measurements (18 O iii λ4363, 29 N ii λ5755, 40 S iiiλ6312, and 40 O ii λλ7320, 7330 detections) in 45 H ii regions. Comparing derived temperatures from multiple auroral line measurements, we find: (1) a strong correlation between temperatures based on S iii λ6312 and N ii λ5755; and (2) large discrepancies for some temperatures based on O ii λλ7320, 7330 and O iii λ4363. Both of these trends are consistent with other observations in the literature, yet, given the widespread use and acceptance of O iii λ4363 as a temperature determinant, the magnitude of the TO iii discrepancies still came as a surprise. Based on these results, we conduct a uniform abundance analysis prioritizing the temperatures derived from S iii λ6312 and N ii λ5755, and report the gas-phase abundance gradients for NGC 628. Relative abundances of S/O, Ne/O, and Ar/O are constant across the galaxy, consistent with no systematic change in the upper IMF over the sampled range in metallicity. These alpha-element ratios, along with N/O, all show small dispersions ( ∼ 0.1 dex) over 70% of the azimuthally averaged radius. We interpret these results as an indication that, at a given radius, the interstellar medium in NGC 628 is chemically well-mixed. Unlike the gradients in the nearly temperature-independent relative abundances, O/H abundances have a larger intrinsic dispersion of ∼0.165 dex. We posit that this dispersion represents an upper limit to the true dispersion in O/H at a given radius and that some of that dispersion is due to systematic uncertainties arising from temperature measurements.
ABSTRACT
We present measurements of the redshift-dependent clustering of a DESI-like luminous red galaxy (LRG) sample selected from the Legacy Survey imaging data set, and use the halo occupation ...distribution (HOD) framework to fit the clustering signal. The photometric LRG sample in this study contains 2.7 million objects over the redshift range of 0.4 < z < 0.9 over 5655 deg2. We have developed new photometric redshift (photo-z) estimates using the Legacy Survey DECam and WISE photometry, with σNMAD = 0.02 precision for LRGs. We compute the projected correlation function using new methods that maximize signal-to-noise ratio while incorporating redshift uncertainties. We present a novel algorithm for dividing irregular survey geometries into equal-area patches for jackknife resampling. For a five-parameter HOD model fit using the MultiDark halo catalogue, we find that there is little evolution in HOD parameters except at the highest redshifts. The inferred large-scale structure bias is largely consistent with constant clustering amplitude over time. In an appendix, we explore limitations of Markov chain Monte Carlo fitting using stochastic likelihood estimates resulting from applying HOD methods to N-body catalogues, and present a new technique for finding best-fitting parameters in this situation. Accompanying this paper, we have released the Photometric Redshifts for the Legacy Surveys catalogue of photo-z’s obtained by applying the methods used in this work to the full Legacy Survey Data Release 8 data set. This catalogue provides accurate photometric redshifts for objects with z < 21 over more than 16 000 deg2 of sky.
The chemical abundances of spiral galaxies, as probed by H ii regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present Large ...Binocular Telescope/Multi-Object Double Spectrographs spectra of 52 H ii regions in NGC 3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral-line detections in 190 individual H ii regions. We find that the dispersion in relationships is dependent on ionization, as characterized by , and so we recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that N ii and S iii provide the most robust measures of electron temperature in low-ionization zones, while O iii provides reliable electron temperatures in high-ionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical integral field unit studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of dex/Re with tot. = 0.08 for Rg/Re < 2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O-O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich H ii regions.
We study the nature of feedback mechanisms in the 11 CLASH brightest cluster galaxies (BCGs) that exhibit extended ultraviolet and nebular line emission features. We estimate star formation rates ...(SFRs), dust masses, and starburst durations using a Bayesian photometry-fitting technique that accounts for both stellar and dust emission from the UV through far-IR. By comparing these quantities to intracluster medium (ICM) cooling times and freefall times derived from X-ray observations and lensing estimates of the cluster mass distribution, we discover a tight relationship between the BCG SFR and the ICM cooling time to freefall time ratio, , with an upper limit on the intrinsic scatter of 0.15 dex. Furthermore, starburst durations may correlate with ICM cooling times at a radius of , and the two quantities converge upon reaching the gigayear regime. Our results provide a direct observational link between the thermodynamical state of the ICM and the intensity and duration of BCG star formation activity, and appear consistent with a scenario where active galactic nuclei induce condensation of thermally unstable ICM overdensities that fuel long-duration (>1 Gyr) BCG starbursts. This scenario can explain (a) how gas with a low cooling time is depleted without causing a cooling flow and (b) the scaling relationship between SFR and . We also find that the scaling relation between SFR and dust mass in BCGs with SFRs yr−1 is similar to that in star-forming field galaxies; BCGs with large ( yr−1) SFRs have dust masses comparable to extreme starbursts.
ABSTRACT We calibrate the integrated luminosity from the polycyclic aromatic hydrocarbon (PAH) features at 6.2, 7.7, and 11.3 m in galaxies as a measure of the star formation rate (SFR). These ...features are strong (containing as much as 5%-10% of the total infrared luminosity) and suffer minimal extinction. Our calibration uses Spitzer Infrared Spectrograph (IRS) measurements of 105 galaxies at 0 < z < 0.4, infrared (IR) luminosities of 109-1012 , combined with other well-calibrated SFR indicators. The PAH luminosity correlates linearly with the SFR as measured by the extinction-corrected H luminosity over the range of luminosities in our calibration sample. The scatter is 0.14 dex, comparable to that between SFRs derived from the Pa and extinction-corrected H emission lines, implying that the PAH features may be as accurate an SFR indicator as hydrogen recombination lines. The PAH SFR relation depends on gas-phase metallicity, for which we supply an empirical correction for galaxies with 0.2 < Z 0.7 . We present a case study in advance of the James Webb Space Telescope (JWST), which will be capable of measuring SFRs from PAHs in distant galaxies at the peak of the SFR density in the universe (z ∼ 2) with SFRs as low as ∼10 . We use Spitzer/IRS observations of the PAH features and Pa emission plus H measurements in lensed star-forming galaxies at 1 < z < 3 to demonstrate the ability of the PAHs to derive accurate SFRs. We also demonstrate that because the PAH features dominate the mid-IR fluxes, broadband mid-IR photometric measurements from JWST will both trace the SFR and provide a way to exclude galaxies dominated by an active galactic nucleus.
CHAOS. II. GAS-PHASE ABUNDANCES IN NGC 5194 Croxall, Kevin V.; Pogge, Richard W.; Berg, Danielle A. ...
Astrophysical journal/The Astrophysical journal,
07/2015, Letnik:
808, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We have observed NGC 5194 (M51a) as part of the CHemical Abundances of Spirals project. Using the Multi Object Double Spectrographs on the Large Binocular Telescope we are able to measure ...one or more of the temperature-sensitive auroral lines (O iii λ4363, N ii λ5755, S iii λ6312) and thus measure "direct" gas-phase abundances in 29 individual H ii regions. O iii λ4363 is only detected in two H ii regions, both of which show indications of excitation by shocks. We compare our data to previous direct abundances measured in NGC 5194 and find excellent agreement ( ) for all but one region. We find no evidence of trends in Ar/O, Ne/O, or S/O within NGC 5194 or compared to other galaxies. We find modest negative gradients in both O/H and N/O with very little scatter ( ≤ 0.08 dex), most of which can be attributed to random error and not to intrinsic dispersion. The gas-phase abundance gradient is consistent with the gradients observed in other interacting galaxies, which tend to be shallower than gradients measured in isolated galaxies. The N/O ratio ( ) suggests secondary nitrogen production is responsible for a significantly larger fraction of nitrogen (e.g., factor of 8-10), relative to primary production mechanisms than predicted by theoretical models.
We present results on the clustering properties of galaxies as a function of both stellar mass and specific star formation rate (sSFR) using data from the PRIMUS and DEEP2 galaxy redshift surveys ...spanning . We use spectroscopic redshifts of over 100,000 galaxies covering an area of 7.2 deg2 over five separate fields on the sky, from which we calculate cosmic variance errors. We find that the galaxy clustering amplitude is as strong of a function of sSFR as of stellar mass, and that at a given sSFR, it does not significantly depend on stellar mass within the range probed here. We further find that within the star-forming population and at a given stellar mass, galaxies above the main sequence of star formation with higher sSFR are less clustered than galaxies below the main sequence with lower sSFR. We also find that within the quiescent population, galaxies with higher sSFR are less clustered than galaxies with lower sSFR, at a given stellar mass. We show that the galaxy clustering amplitude smoothly increases with both increasing stellar mass and decreasing sSFR, implying that galaxies likely evolve across the main sequence, not only along it, before galaxies eventually become quiescent. These results imply that the relation of stellar mass to halo mass, which connects galaxies to dark matter halos, likely depends on sSFR.
PDF
