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Register a new userDissecting the complex environment of a distant quasar with MUSE
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High redshift quasars can be used to trace the early growth of massive galaxies and may be triggered by galaxy-galaxy interactions. We present MUSE science verification data on one such interacting system consisting of the well-studied z=3.2 PKS1614+051 quasar, its AGN companion galaxy and bridge of material radiating in Lyalpha between the quasar and its companion. We find a total of four companion galaxies (at least two galaxies are new discoveries), three of which reside within the likely virial radius of the quasar host, suggesting that the system will evolve into a massive elliptical galaxy by the present day. The MUSE data are of sufficient quality to split the extended Lyalpha emission line into narrow velocity channels. In these the gas can be seen extending towards each of the three neighbouring galaxies suggesting that the emission-line gas originates in a gravitational interaction between the galaxies and the quasar host. The photoionization source of this gas is less clear but is probably dominated by the two AGN. The quasars Lyalpha emission spectrum is double-peaked, likely due to absorbing neutral material at the quasars systemic redshift with a low column density as no damping wings are present. The spectral profiles of the AGN and bridges Lyalpha emission are also consistent with absorption at the same redshift indicating this neutral material may extend over > 50 kpc. The fact that the neutral material is seen in the line of sight to the quasar and transverse to it, and the fact that we see the quasar and it also illuminates the emission-line bridge, suggests the quasar radiates isotropically and any obscuring torus is small. These results demonstrate the power of MUSE for investigating the dynamics of interacting systems at high redshift.
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AT 2018cow was the nearest and best studied example of a new breed of extra-galactic, luminous and rapidly-evolving transient. Both the progenitor systems and explosion mechanisms of these rapid transients remain a mystery - the energetics, spectral signatures, and timescales make them challenging to interpret in established classes of supernovae and tidal disruption events. The rich, multi-wavelength data-set of AT 2018cow has still left several interpretations viable to explain the nature of this event. In this paper we analyse integral-field spectroscopic data of the host galaxy, CGCG 137-068, to compare environmental constraints with leading progenitor models. We find the explosion site of AT 2018cow to be very typical of core-collapse supernovae (known to form from stars with MZAMS ~8-25M), and infer a young stellar population age at the explosion site of few times 10Myr, at slightly sub-solar metallicity. When comparing to expectations for exotic intermediate-mass black hole (IMBH) tidal disruption events,we find no evidence for a potential host system of the IMBH. In particular, there are no abrupt changes in metallicity or kinematics in the vicinity of the explosion site, arguing against the presence of a distinct host system. The proximity of AT 2018cow to strong star-formation in the host galaxy makes us favour a massive stellar progenitor for this event.
We present results of the MUSE-ALMA Halos, an ongoing study of the Circum-Galactic Medium (CGM) of low redshift galaxies (z < 1.4), currently comprising 14 strong HI absorbers in five quasar fields. We detect 43 galaxies associated with absorbers down to star formation rate (SFR) limits of 0.01-0.1 solar masses/yr, found within impact parameters (b) of 250 kpc from the quasar sightline. Excluding the targeted absorbers, we report a high detection rate of 89 per cent and find that most absorption systems are associated with pairs or groups of galaxies (three to eleven members). We note that galaxies with the smallest impact parameters are not necessarily the closest to the absorbing gas in velocity space. Using a multi-wavelength dataset (UVES/HIRES, HST, MUSE), we combine metal and HI column densities, allowing for derivation of the lower limits of neutral gas metallicity as well as emission line diagnostics (SFR, metallicities) of the ionised gas in the galaxies. We find that groups of associated galaxies follow the canonical relations of N(HI) -- b and W_r(2796) -- b, defining a region in parameter space below which no absorbers are detected. The metallicity of the ISM of associated galaxies, when measured, is higher than the metallicity limits of the absorber. In summary, our findings suggest that the physical properties of the CGM of complex group environments would benefit from associating the kinematics of individual absorbing components with each galaxy member.
We present a study of cold gas absorption from a damped Lyman-$alpha$ absorber (DLA) at redshift $z_{rm abs}=1.946$ towards two lensed images of the quasar J144254.78+405535.5 at redshift $z_{rm QSO} = 2.590$. The physical separation of the two lines of sight at the absorber redshift is $d_{rm abs}=0.7$~kpc based on our lens model. We observe absorption lines from neutral carbon and H$_2$ along both lines of sight indicating that cold gas is present on scales larger than $d_{rm abs}$. We measure column densities of HI to be $log N(rm H,i) = 20.27pm0.02$ and $20.34pm0.05$ and of H$_2$ to be $log N(rm H_2) = 19.7pm0.1$ and $19.9pm0.2$. The metallicity inferred from sulphur is consistent with Solar metallicity for both sightlines: $[{rm S/H}]_A = 0.0pm0.1$ and $[{rm S/H}]_B = -0.1pm0.1$. Based on the excitation of low rotational levels of H$_2$, we constrain the temperature of the cold gas phase to be $T=109pm20$ and $T=89pm25$ K for the two lines of sight. From the relative excitation of fine-structure levels of CI, we constrain the hydrogen volumetric densities in the range of $40-110$ cm$^{-3}$. Based on the ratio of observed column density and volumetric density, we infer the average individual `cloud size along the line of sight to be $lapprox0.1$ pc. Using the transverse line-of-sight separation of 0.7 kpc together with the individual cloud size, we are able to put an upper limit to the volume filling factor of cold gas of $f_{rm vol} < 0.2$ %. Nonetheless, the projected covering fraction of cold gas must be large (close to unity) over scales of a few kpc in order to explain the presence of cold gas in both lines of sight. Compared to the typical extent of DLAs (~10-30 kpc), this is consistent with the relative incidence rate of CI absorbers and DLAs.
We present a high-resolution analysis of the host galaxy of fast radio burst FRB 190608, an SBc galaxy at $z=0.11778$ (hereafter HG 190608), to dissect its local environment and its contributions to the FRB properties. Our Hubble Space Telescope WFC3/UVIS image reveals that the sub-arcsecond localization of FRB 190608 is coincident with a knot of star-formation ($Sigma_{SFR} = 1.2 times 10^{-2}~ M_{odot} , kpc^{-2}$) in one of the prominent spiral arms of HG 190608. This is confirmed by H$beta$ emission present in our Keck/KCWI integral field spectrum of the galaxy with a surface brightness of $mu_{Hbeta} = (3.35pm0.18)times10^{-17};erg;s^{-1};cm^{-2};arcsec^{-2}$. We infer an extinction-corrected H$alpha$ surface brightness and compute a dispersion measure from the interstellar medium of HG 190608 of ${DM}_{Host,ISM} = 82 pm 35~ pc , cm^{-3}$. The galaxy rotates with a circular velocity $v_{circ} = 141 pm 8~ km , s^{-1}$ at an inclination $i_{gas} = 37 pm 3^circ$, giving a dynamical mass $M_{halo}^{dyn} approx 10^{11.96 pm 0.08}~ M_{odot}$. A surface photometric analysis of the galaxy using FORS2 imaging suggests a stellar disk inclination of $i_{stellar} = 26 pm 3^circ$. The dynamical mass estimate implies a halo contribution to the dispersion measure of ${DM}_{Host,Halo} = 55 pm 25; pc , cm^{-3}$ subject to assumptions on the density profile and fraction of baryons retained. The relatively high temporal broadening ($tau = 3.3 pm 0.2 ; ms$ at 1.28 GHz) and rotation measure ($ RM = 353 pm 2; rad ; m^{-2}$) (Day et al. 2020) of FRB 190608 may be attributable to both turbulent gas within the spiral arm and gas local to the FRB progenitor. In contrast to previous high-resolution studies of FRB progenitor environments, we find no evidence for disturbed morphology, emission, nor kinematics for FRB 190608.
We report observations with the Atacama Large Millimetre Array (ALMA) of six submillimetre galaxies (SMGs) within 3 arcmin of the Distant Red Core (DRC) at $z=4.0$, a site of intense cluster-scale star formation, first reported by Oteo et al. (2018). We find new members of DRC in three SMG fields; in two fields, the SMGs are shown to lie along the line of sight towards DRC; one SMG is spurious. Although at first sight this rate of association is consistent with earlier predictions, associations with the bright SMGs are rarer than expected, which suggests caution when interpreting continuum over-densities. We consider the implications of all 14 confirmed DRC components passing simultaneously through an active phase of star formation. In the simplest explanation, we see only the tip of the iceberg in terms of star formation and gas available for future star formation, consistent with our remarkable finding that the majority of newly confirmed DRC galaxies are not the brightest continuum emitters in their immediate vicinity. Thus while ALMA continuum follow-up of SMGs identifies the brightest continuum emitters in each field, it does not necessarily reveal all the gas-rich galaxies. To hunt effectively for protocluster members requires wide and deep spectral-line imaging to uncover any relatively continuum-faint galaxies that are rich in atomic or molecular gas. Searching with short-baseline arrays or single-dish facilities, the true scale of the underlying gas reservoirs may be revealed.
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