23 research outputs found

    HST Detection of Extended Neutral Hydrogen in a Massive Elliptical at z = 0.4

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    We report the first detection of extended neutral hydrogen (HI) gas in the interstellar medium (ISM) of a massive elliptical galaxy beyond z~0. The observations utilize the doubly lensed images of QSO HE 0047-1756 at z_QSO = 1.676 as absorption-line probes of the ISM in the massive (M_star ~ 10^11 M_sun) elliptical lens at z = 0.408, detecting gas at projected distances of d = 3.3 and 4.6 kpc on opposite sides of the lens. Using the Space Telescope Imaging Spectrograph (STIS), we obtain UV absorption spectra of the lensed QSO and identify a prominent flux discontinuity and associated absorption features matching the Lyman series transitions at z = 0.408 in both sightlines. The HI column density is log N(HI) = 19.6-19.7 at both locations across the lens, comparable to what is seen in 21 cm images of nearby ellipticals. The HI gas kinematics are well-matched with the kinematics of the FeII absorption complex revealed in ground-based echelle data, displaying a large velocity shear of 360 km/s across the galaxy. We estimate an ISM Fe abundance of 0.3-0.4 solar at both locations. Including likely dust depletions increases the estimated Fe abundances to solar or supersolar, similar to those of the hot ISM and stars of nearby ellipticals. Assuming 100% covering fraction of this Fe-enriched gas,we infer a total Fe mass of M_cool(Fe)~(5-8)x10^4 M_sun in the cool ISM of the massive elliptical lens, which is no more than 5% of the total Fe mass observed in the hot ISM.Comment: 6 pages, 2 figures; Accepted for publication in ApJ Letter

    Evidence for Late-Time Feedback from the Discovery of Multiphase Gas in a Massive Elliptical at z=0.4z=0.4

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    We report the first detection of multiphase gas within a quiescent galaxy beyond z≈0z\approx0. The observations use the brighter image of doubly lensed QSO HE 0047−-1756 to probe the ISM of the massive (Mstar≈1011M⊙M_{\rm star}\approx 10^{11} \mathrm{M_\odot}) elliptical lens galaxy at zgal=0.408z_\mathrm{gal}=0.408. Using Hubble Space Telescope's Cosmic Origins Spectrograph (COS), we obtain a medium-resolution FUV spectrum of the lensed QSO and identify numerous absorption features from H2\mathrm{H_2} in the lens ISM at projected distance d=4.6d=4.6 kpc. The H2\mathrm{H_2} column density is log⁡N(H2)/cm−2=17.8−0.3+0.1\log N(\mathrm{H_2})/\mathrm{cm^{-2}}=17.8^{+0.1}_{-0.3} with a molecular gas fraction of fH2=2−5%f_\mathrm{H_2}=2-5\%, roughly consistent with some local quiescent galaxies. The new COS spectrum also reveals kinematically complex absorption features from highly ionized species O VI and N V with column densities log N(OVI)/cm−2=15.2±0.1N(\mathrm{O VI})/\mathrm{cm^{-2}} =15.2\pm0.1 and log N(NV)/cm−2=14.6±0.1N(\mathrm{N V})/\mathrm{cm^{-2}} =14.6\pm0.1, among the highest known in external galaxies. Assuming the high-ionization absorption features originate in a transient warm (T∼105 T\sim10^5\,K) phase undergoing radiative cooling from a hot halo surrounding the galaxy, we infer a mass accretion rate of ∼0.5−1.5 M⊙ yr−1\sim 0.5-1.5\,\mathrm{M_\odot\,yr^{-1}}. The lack of star formation in the lens suggests the bulk of this flow is returned to the hot halo, implying a heating rate of ∼1048 erg yr−1\sim10^{48}\,\mathrm{erg\,yr^{-1}}. Continuous heating from evolved stellar populations (primarily SNe Ia but also winds from AGB stars) may suffice to prevent a large accumulation of cold gas in the ISM, even in the absence of strong feedback from an active nucleus.Comment: 10 pages, 4 figures. Accepted for publication in ApJ Letters following a minor revisio

    Characterizing Circumgalactic Gas around Massive Ellipticals at z~0.4 - II. Physical Properties and Elemental Abundances

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    We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d<160 kpc of luminous red galaxies (LRGs). The sample comprises 16 intermediate-redshift (z=0.21-0.55) LRGs of stellar mass M_star>1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full HI Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually-matched components, we show that cool gas (T~1e4 K) density and metallicity can vary by more than a factor of ten in in an LRG halo. Specifically, metal-poor absorbing components with <1/10 solar metallicity are seen in 50% of the LRG halos, while gas with solar and super-solar metallicity is also common. These results indicate a complex multiphase structure and poor chemical mixing in these quiescent halos. We calculate the total surface mass density of cool gas, \Sigma_cool, by applying the estimated ionization fraction corrections to the observed HI column densities. The radial profile of \Sigma_cool is best-described by a projected Einasto profile of slope \alpha=1 and scale radius r_s=48 kpc. We find that typical LRGs at z~0.4 contain cool gas mass of M_cool= (1-2) x1e10 M_sun at d<160 kpc (or as much as 4x1e10 M_sun at d<500 kpc), comparable to the cool CGM mass of star-forming galaxies. Furthermore, we show that high-ionization OVI and low-ionization absorption species exhibit distinct velocity profiles, highlighting their different physical origins. We discuss the implications of our findings for the origin and fate of cool gas in LRG halos.Comment: Accepted for publication in MNRAS after a minor revision. 23 pages, 14 figures, and a 29-page Appendix with 27 additional figure

    Characterizing Circumgalactic Gas around Massive Ellipticals at z ~ 0.4 I. Initial Results

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    We present a new Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) absorption-line survey to study halo gas around 16 luminous red galaxies (LRGs) at z=0.21-0.55. The LRGs are selected uniformly with stellar mass Mstar>1e11 Msun and no prior knowledge of the presence/absence of any absorption features. Based on observations of the full Lyman series, we obtain accurate measurements of neutral hydrogen column density N(HI) and find that high-N(HI) gas is common in these massive quiescent halos with a median of <log N(HI)> = 16.6 at projected distances d<~160 kpc. We measure a mean covering fraction of optically-thick gas with log N(HI)>~17.2 of LLS=0.44^{+0.12}_{-0.11} at d<~160 kpc and LLS=0.71^{+0.11}_{-0.20} at d<~100 kpc. The line-of-sight velocity separations between the HI absorbing gas and LRGs are characterized by a mean and dispersion of =29 km/s and \sigma_v_{gas-gal}=171 km/s. Combining COS FUV and ground-based echelle spectra provides an expanded spectral coverage for multiple ionic transitions, from low-ionization MgII and SiII, to intermediate ionization SiIII and CIII, and to high-ionization OVI absorption lines. We find that intermediate ions probed by CIII and SiIII are the most prominent UV metal lines in LRG halos with a mean covering fraction of _{0.1}=0.75^{+0.08}_{-0.13} for W(977)>=0.1 Ang at d<160 kpc, comparable to what is seen for CIII in L* and sub-L* star-forming and red galaxies but exceeding MgII or OVI in quiescent halos. The COS-LRG survey shows that massive quiescent halos contain widespread chemically-enriched cool gas and that little distinction between LRG and star-forming halos is found in their HI and CIII content.Comment: 19 pages, 6 figures, accepted by MNRA

    EMPRESS. VI. Outflows Investigated in Low-Mass Galaxies with M∗=104−107 M⊙M_*=10^4-10^7~M_\odot: Weak Feedback in Low-Mass Galaxies?

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    We study emission line profiles of 21 nearby low-mass (M∗=104−107 M⊙M_*=10^4-10^7~M_\odot) galaxies in deep medium-high resolution spectra taken with Magellan/MagE. These low-mass galaxies are actively star-forming systems with high specific star-formation rates of sSFR∼100−1000 Gyr−1\mathrm{sSFR}\sim100-1000~\mathrm{Gyr}^{-1} that are well above the star-formation main sequence and its extrapolation. We identify broad-line components of Hα\alpha and [OIII]λ5007\lambda 5007 emission in 14 out of the 21 galaxies that cannot be explained by the MagE instrumental profile or the natural broadening of line emission. We conduct double Gaussian profile fitting to the emission of the 14 galaxies, and find that the broad-line components have line widths significantly larger than those of the narrow-line components, indicative of galactic outflows. The board-line components have moderately large line widths of ∼100\sim 100 km s−1^{-1}. We estimate the maximum outflow velocities vmaxv_\mathrm{max} and obtain values of ≃60−200\simeq 60-200 km s−1^{-1}, which are found to be comparable to or slightly larger than the escape velocities. Positive correlations of vmaxv_\mathrm{max} with star-formation rates, stellar masses, and circular velocities, extend down into this low-mass regime. Broad- to narrow-line flux ratios BNRs are generally found to be smaller than those of massive galaxies. The small vmaxv_\mathrm{max} and BNRs suggest that the mass loading factors η\eta can be as small as 0.1 - 1 or below, in contrast to the large η\eta of energy-driven outflows predicted by numerical simulations.Comment: 22 pages, 11 figures, Accepted for publication by Ap

    The Cosmic Ultraviolet Baryon Survey (CUBS) I. Overview and the diverse environments of Lyman limit systems at z<1

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    We present initial results from the Cosmic Ultraviolet Baryon Survey (CUBS). CUBS is designed to map diffuse baryonic structures at redshift z<~1 using absorption-line spectroscopy of 15 UV-bright QSOs with matching deep galaxy survey data. CUBS QSOs are selected based on their NUV brightness to avoid biases against the presence of intervening Lyman Limit Systems (LLSs) at zabs~ 17.2 over a total redshift survey pathlength of dz=9.3, and a number density of n(z)=0.43 (-0.18, +0.26). Considering all absorbers with log N(HI)/cm^-2 > 16.5 leads to n(z)=1.08 (-0.25, +0.31) at z<1. All LLSs exhibit a multi-component structure and associated metal transitions from multiple ionization states such as CII, CIII, MgII, SiII, SiIII, and OVI absorption. Differential chemical enrichment levels as well as ionization states are directly observed across individual components in three LLSs. We present deep galaxy survey data obtained using the VLT-MUSE integral field spectrograph and the Magellan Telescopes, reaching sensitivities necessary for detecting galaxies fainter than 0.1L* at d<~300 physical kpc (pkpc) in all five fields. A diverse range of galaxy properties is seen around these LLSs, from a low-mass dwarf galaxy pair, a co-rotating gaseous halo/disk, a star-forming galaxy, a massive quiescent galaxy, to a galaxy group. The closest galaxies have projected distances ranging from d=15 to 72 pkpc and intrinsic luminosities from ~0.01L* to ~3L*. Our study shows that LLSs originate in a variety of galaxy environments and trace gaseous structures with a broad range of metallicities.Comment: 26 pages, 14 figures, MNRAS in pres