arXiv subjects

Wolfram Kollatschny

Publications and source records attributed to Wolfram Kollatschny.

At least 37 records · Page 2Linked to original sources

arXiv2023

The Stellar Mass - Black Hole Mass Relation at $z\sim2$ Down to $\mathcal{M}_\mathrm{BH}\sim10^7 M_\odot$ Determined by HETDEX

We investigate the stellar mass - black hole mass ($\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$) relation with type 1 AGN down to $\mathcal{M}_\mathrm{BH}=10^7 M_\odot$, corresponding to a $\simeq -21$ absolute magnitude in rest-frame ultraviolet (UV), at $z = 2-2.5$. Exploiting the deep and large-area spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), we identify 66 type 1 AGN with $\mathcal{M}_\mathrm{BH}$ ranging from $10^7$ to $10^{10} M_\odot$ that are measured with single-epoch virial method using C{\sc iv} emission lines detected in the HETDEX spectra. $\mathcal{M}_*$ of the host galaxies are estimated from optical to near-infrared photometric data taken with Spitzer, WISE, and ground-based 4-8m class telescopes by CIGALE SED fitting. We further assess the validity of SED fitting in two cases by host-nuclear decomposition performed through surface brightness profile fitting on spatially-resolved host galaxies with JWST/NIRCam CEERS data. We obtain the $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation covering the unexplored low-mass ranges of $\mathcal{M}_\mathrm{BH}~\sim~10^7-10^8~M_\odot$, and conduct forward modelling to fully account for the selection biases and observational uncertainties. The intrinsic $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation at $z\sim 2$ has a moderate positive offset of $0.52\pm0.14$~dex from the local relation, suggestive of more efficient black hole growth at higher redshift even in the low-mass regime of $\mathcal{M}_\mathrm{BH}~\sim~10^7-10^8~M_\odot$. Our $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation is inconsistent with the $\mathcal{M}_\mathrm{BH}$ suppression at the low-$\mathcal{M}_*$ regime predicted by recent hydrodynamic simulations at a $98\%$ confidence level, suggesting that feedback in the low-mass systems may be weaker than those produced in hydrodynamic simulations.

astro-ph.GA↗

arXiv2023

HETDEX Public Source Catalog 1: 220K Sources Including Over 50K Lyman Alpha Emitters from an Untargeted Wide-area Spectroscopic Survey

We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88<z<3.52 by using the spatial distribution of more than a million Ly-alpha-emitting galaxies over a total target area of 540 deg^2. The catalog comes from contiguous fiber spectra coverage of 25 deg^2 of sky from January 2017 through June 2020, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Lyα-emitting galaxy (LAE) identifications and 123,891 OII-emitting galaxies at z<0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift (z<0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, OII and Ly-alpha line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within deltaz < 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE sample has an r-band continuum counterpart down to a limiting magnitude of r~26.2 mag (AB) indicating that an LAE search of similar sensitivity with photometric pre-selection would miss nearly half of the HETDEX LAE catalog sample. Data access and details about the catalog can be found online at http://hetdex.org/.

astro-ph.GA↗

arXiv2023

The HETDEX Survey: Emission Line Exploration and Source Classification

The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is an untargeted spectroscopic survey that aims to measure the expansion rate of the Universe at $z \sim 2.4$ to 1% precision for both $H(z)$ and $D_A(z)$. HETDEX is in the process of mapping in excess of one million Lyman Alpha emitting (LAE) galaxies and a similar number of lower-z galaxies as a tracer of the large-scale structure. The success of the measurement is predicated on the post-observation separation of galaxies with Ly$α$ emission from the lower-$z$ interloping galaxies, primarily [OII], with low contamination and high recovery rates. The Emission Line eXplorer (ELiXer) is the principal classification tool for HETDEX, providing a tunable balance between contamination and completeness as dictated by science needs. By combining multiple selection criteria, ELiXer improves upon the 20 Angstrom rest-frame equivalent width cut commonly used to distinguish LAEs from lower-$z$ [OII] emitting galaxies. Despite a spectral resolving power, R $\sim800$, that cannot resolve the [OII] doublet, we demonstrate the ability to distinguish LAEs from foreground galaxies with 98.1% accuracy. We estimate a contamination rate of Ly$α$ by [OII] of 1.2% and a Ly$α$ recovery rate of 99.1% using the default ELiXer configuration. These rates meet the HETDEX science requirements.

astro-ph.GA↗

arXiv2022

The outburst of the changing-look AGN IRAS23226-3843 in 2019

IRAS23226-3843 has previously been classified as a changing-look AGN based on X-ray and optical spectral variations. In 2019, Swift observations revealed a strong rebrightening in X-ray and UV fluxes in comparison to observations in 2017. We took follow-up Swift, XMM-Newton, and NuSTAR observations together with optical spectra (SALT and SAAO 1.9m telescope) from 2019 until 2021. IRAS23226-3843 showed a strong X-ray and optical outburst in 2019. It varied in the X-ray and optical continuum by a factor of 5 and 1.6, respectively, within two months. This corresponds to a factor of 3 in the optical after correction for the host galaxy contribution. The Balmer and FeII emission-line intensities showed comparable variability amplitudes. The Halpha profiles changed from a blue-peaked profile in the years 1997 and 1999 to a broad double-peaked profile in 2017 and 2019. However, there were no major profile variations in the extremely broad double-peaked profiles despite the strong intensity variations in 2019. One year after the outburst, the optical spectral type changed and became a Seyfert type 2 in 2020. Blue outflow components are present in the Balmer lines and in the Fe band in the X-rays. A deep broadband XMM-Newton/NuSTAR spectrum was taken during the maximum state in 2019. This spectrum is qualitatively very similar to a spectrum taken in 2017, but by a factor of 10 higher. The soft X-ray band appears featureless. The soft excess is well modeled with a Comptonization model. A broadband fit with a power-law continuum, Comptonized soft excess, and Galactic absorption gives a good fit to the combined EPIC-pn and NuSTAR spectrum. In addition, we see a complex and broadened Fe K emission-line profile in the X-rays. The changing-look character in IRAS23226-3843 is most probably caused by changes in the accretion rate -- based on the short-term variations on timescales of weeks to months.

astro-ph.HE↗

arXiv2022

The MUSE Hubble Ultra Deep Field surveys: Data release II

We present the second data release of the MUSE Hubble UDF surveys, which includes the deepest spectroscopic survey ever performed. The MUSE data, with their 3D content, amazing depth, wide spectral range, and excellent spatial and medium spectral resolution, are rich in information. This update of the first release incorporates a new 141-hour adaptive-optics-assisted MXDF field (1' diameter FoV) in addition to the reprocessed 10-hour mosaic (3'x3') and the single 31-hour deep field (1'x1'). We have securely identified and measured the redshift of 2221 sources, an increase of 41% compared to the first release. With the exception of 8 stars, the collected sample consists of 25 nearby galaxies (z < 0.25), 677 OII emitters (z=0.25-1.5), 201 galaxies in the MUSE redshift desert range (z=1.5-2.8), and 1308 LAEs (z=2.8-6.7). This represents an order of magnitude more redshifts than the collection of all spectroscopic redshifts obtained before MUSE in the Hubble UDF area (2221 vs 292). At z > 3, the difference is even more striking, with a factor of 65 increase (1308 vs 20). We compared the measured redshifts against three published photometric redshift catalogs and find the photo-z accuracy to be lower than the constraints provided by photo-z fitting codes. 80% of the galaxies have an HST counterpart. They are on average faint, with a median magnitude of 25.7 and 28.7 for the OII and Ly-alpha emitters, respectively. SED fits show that these galaxies tend to be low-mass star-forming galaxies, with a median stellar mass of 6.2 10**8 M and a median SFR of 0.4 M/yr. 20% of our catalog, or 424 galaxies, have no HST counterpart. The vast majority of these new sources are high EQW z>2.8 LAEs that are detected by MUSE thanks to their bright and asymmetric broad Ly-alpha line. We release advanced data products, specific software, and a web interface to select and download data sets.

astro-ph.GA↗

arXiv2022

Directly tracing cool filamentary accretion over >100 kpc into the interstellar medium of a quasar host at z=1

We report the discovery of giant (50-100 kpc) [O II] emitting nebulae with the Multi-Unit Spectroscopic Explorer (MUSE) in the field of TXS 0206-048, a luminous quasar at z=1.13. Down-the-barrel UV spectra of the quasar show absorption at velocities coincident with those of the extended nebulae, enabling new insights into inflows and outflows around the quasar host. One nebula exhibits a filamentary morphology extending over 120 kpc from the halo toward the quasar and intersecting with another nebula surrounding the quasar host with a radius of 50 kpc. This is the longest cool filament observed to-date and arises at higher redshift and in a less massive system than those in cool-core clusters. The filamentary nebula has line-of-sight velocities >300 km/s from nearby galaxies but matches that of the nebula surrounding the quasar host where they intersect, consistent with accretion of cool inter- or circum-galactic medium or cooling hot halo gas. The kinematics of the nebulae surrounding the quasar host are unusual and complex, with redshifted and blueshifted spiral-like structures. The emission velocities at 5-10 kpc from the quasar match those of inflowing absorbing gas observed in UV spectra of the quasar. Together, the extended nebulae and associated redshifted absorption represent a compelling case of cool, filamentary gas accretion from halo scales into the extended interstellar medium and toward the nucleus of a massive quasar host. The inflow rate implied by the combined emission and absorption constraints is well below levels required to sustain the quasar's radiative luminosity, suggesting anisotropic or variable accretion.

astro-ph.GA↗

arXiv2022

The Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) III. A red quasar with extremely high equivalent widths showing powerful outflows

We report an Active Galactic Nucleus (AGN) with extremely high equivalent width (EW), EW(LyA+NV,rest)>921 AA in the rest-frame, at z~2.24 in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) as a representative case of the high EW AGN population. The continuum level is a non-detection in the HETDEX spectrum, thus the measured EW is a lower limit. The source is detected with significant emission lines (>7sigma) at LyA+NV, CIV, and moderate emission line (~4sigma) at HeII within the wavelength coverage of HETDEX (3500 AA - 5500 AA). The r-band magnitude is 24.57 from the Hyper Suprime-Cam-HETDEX joint survey with a detection limit of r=25.12 at 5sigma. The LyA emission line spans a clearly resolved region of ~10 arcsec (85 kpc) in diameter. The LyA line profile is strongly double peaked. The spectral decomposed blue gas and red gas Ly$α$ emission are separated by ~1.2 arcsec (10.1 kpc) with a line-of-sight velocity offset of ~1100 km/s. This source is probably an obscured AGN with powerful winds.

astro-ph.GA↗

arXiv2022

Stellar Populations of Lyman-alpha Emitting Galaxies in the HETDEX Survey I: An Analysis of LAEs in the GOODS-N Field

We present the results of a stellar-population analysis of Lyman-alpha emitting galaxies (LAES) in GOODS-N at 1.9 < z < 3.5 spectroscopically identified by the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We provide a method for connecting emission-line detections from the blind spectroscopic survey to imaging counterparts, a crucial tool needed as HETDEX builds a massive database of ~1 million Lyman-alpha detections. Using photometric data spanning as many as 11 filters covering 0.4-4.5 microns from the Hubble and Spitzer Space Telescopes, we study the objects' global properties and explore which properties impact the strength of Lyman-alpha emission. We measure a median stellar mass of 0.8 (^+2.9_-0.5) x 10^9 Msol and conclude that the physical properties of HETDEX spectroscopically-selected LAEs are comparable to LAEs selected by previous deep narrow band studies. We find that stellar mass and star formation rate correlate strongly with the Lyman-alpha equivalent width. We then use a known sample of z>7 LAEs to perform a proto-study of predicting Lyman-alpha emission from galaxies in the Epoch of Reionization, finding agreement at the 1-sigma level between prediction and observation for the majority of strong emitters.

astro-ph.GA↗

arXiv2022

The Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) II. Luminosity Function

We present the LyA emission line luminosity function (LF) of the Active Galactic Nuclei (AGN) in the first release of the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) AGN catalog (Liu et al. 2022, Paper I). The AGN are selected either by emission-line pairs characteristic of AGN or by single broad emission line, free of any photometric pre-selections (magnitude/color/morphology). The sample consists of 2,346 AGN spanning 1.88 5σ$ confidence at r~26 in the deepest $r$-band images we have searched. The LyA line luminosity ranges from ~10^42.3 to ~10^45.9 erg s^-1. Our LyA LF shows a turnover luminosity with opposite slopes on the bright end and the faint end: The space density is highest at L_LyA^*=10^43.4 erg s^-1. We explore the evolution of the AGN LF over a broader redshift range (0.8<z<3); constructing the rest-frame ultraviolet (UV) LF with the 1450 AA monochromatic luminosity of the power-law component of the continuum ($\rm M_{1450}$) from M_1450~-18 to ~-27.5. We divide the sample into three redshift bins (z~1.5, 2.1, and 2.6). In all three redshift bins, our UV LFs indicate that the space density of AGN is highest at the turnover luminosity M_1450^* with opposite slopes on the bright end and the faint end. The M_1450 LFs in the three redshift bins can be well-fit with a luminosity-evolution-density-evolution (LEDE) model: the turnover luminosity (M_1450^*) increases and the turnover density (Phi^*) decreases with increasing redshift.

astro-ph.GA↗

arXiv2022

The Active Galactic Nuclei in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) I. Sample selection

We present the first Active Galactic Nuclei (AGN) catalog in the Hobby-Eberly Telescope Dark Energy Experiment Survey (HETDEX) observed between January 2017 and June 2020. HETDEX is an ongoing spectroscopic survey with no pre-selection based on magnitudes, colors or morphologies, enabling us to select AGN based on their spectral features. Both luminous quasars and low-luminosity Seyferts are found in our catalog. AGN candidates are selected with at least two significant AGN emission lines, such as the LyA and CIV line pair, or with single broad emission lines (FWHM > 1000 km/s). Each source is further confirmed by visual inspections. This catalog contains 5,322 AGN, covering an effective sky coverage of 30.61 deg^2. A total of 3,733 of these AGN have secure redshifts, and we provide redshift estimates for the remaining 1,589 single broad-line AGN with no cross matched spectral redshifts from SDSS DR14Q. The redshift range of the AGN catalog is 0.25 < z < 4.32, with a median of z = 2.1. The bolometric luminosity range is 10^9-10^14 Lsun with a median of 10^12 Lsun. The median r-band magnitude of the AGN is 21.6 mag, with 34% of the AGN have r > 22.5, and 2.6% reaching the detection limit at r ~ 26 mag of the deepest imaging surveys we searched. We also provide a composite spectrum of the AGN sample covering 700 AA - 4400 AA.

astro-ph.GA↗

arXiv2022

The Great Slump: Mrk926 reveals discrete and varying Balmer line satellite components during a drastic phase of decline

Mrk926 is known to be a highly variable AGN with very broad line profiles. We studied the continuum and line profile variations of this object with high temporal resolution in order to determine its broad-line region structure and to derive its BH mass. We carried out a high-cadence spectroscopic variability campaign of Mrk926 with the 10m HET telescope, aided by photometric V-band data taken at the Wise Observatory, over a period of about five months. We extracted spectroscopic continuum and line light curves, and computed CCFs as well as velocity-resolved CCFs with respect to the combined continuum V-band light curve. The continuum luminosity of Mrk926 showed a drastic decrease during our campaign: it dropped to less than 50% of its original value within only 2.5 months. The spectra show complex and very broad Balmer line profiles, including outer Balmer satellites ranging from +-5000 to +-13,000 kms-1. The Ha, Hb, and HeI5876 line light curves are delayed relative to the continuum light curve. The Ha and Hb lines show two velocity-delay structures in the central part of their line profile (within +- 5000 kms-1), at ~10 and ~57 ld and at ~5 and ~48 ld, respectively. These structures might be interpreted as the signature of a line-emitting ring, inclined by ~50 deg to the line of sight and orbiting the BH at radii, R, of 33.5 and 26.5 ld. We determined continuum luminosities, log(lambda\,L_(lambda)/erg s-1), of 43.68 to 44.13, which are in good agreement with the established R_(BLR)-L_(AGN) relation. We derive a black hole mass of 1.1 +- 0.2 * 10^8 M_solar; this indicates a low Eddington ratio, which decreased from 8 to 3 percent during our campaign. The Balmer satellite components show a response to the continuum variations on the order of only 3-5 days. We attribute this to the central line segment and the Balmer satellites having different, spatially distinct regions of origin.

astro-ph.GA↗

arXiv2021

The MUSE Extremely Deep Field: the Cosmic Web in Emission at High Redshift

We report the discovery of diffuse extended Ly-alpha emission from redshift 3.1 to 4.5, tracing cosmic web filaments on scales of 2.5-4 comoving Mpc. These structures have been observed in overdensities of Ly-alpha emitters in the MUSE Extremely Deep Field, a 140 hour deep MUSE observation located in the Hubble Ultra Deep Field. Among the 22 overdense regions identified, 5 are likely to harbor very extended Ly-alpha emission at high significance with an average surface brightness of $\mathrm{5 \times 10^{-20} erg s^{-1} cm^{-2} arcsec^{-2}}$. Remarkably, 70% of the total Ly-alpha luminosity from these filaments comes from beyond the circumgalactic medium of any identified Ly-alpha emitters. Fluorescent Ly-alpha emission powered by the cosmic UV background can only account for less than 34% of this emission at z$\approx$3 and for not more than 10% at higher redshift. We find that the bulk of this diffuse emission can be reproduced by the unresolved Ly-alpha emission of a large population of ultra low luminosity Ly-alpha emitters ($\mathrm{<10^{40} erg s^{-1}}$), provided that the faint end of the Ly-alpha luminosity function is steep ($α\lessapprox -1.8$), it extends down to luminosities lower than $\mathrm{10^{38} - 10^{37} erg s^{-1}}$ and the clustering of these Ly-alpha emitters is significant (filling factor $< 1/6$). If these Ly-alpha emitters are powered by star formation, then this implies their luminosity function needs to extend down to star formation rates $\mathrm{< 10^{-4} M_\odot yr^{-1}}$. These observations provide the first detection of the cosmic web in Ly-alpha emission in typical filamentary environments and the first observational clue for the existence of a large population of ultra low luminosity Ly-alpha emitters at high redshift.

astro-ph.CO↗

arXiv2020

The MUSE Hubble Ultra Deep Field Survey. XV. The mean rest-UV spectra of Ly-alpha emitters at z>3

We investigate the ultraviolet (UV) spectral properties of faint Lyman-$α$ emitters (LAEs) in the redshift range 2.9 3. We compute various averaged spectra of LAEs sub-sampled on the basis of their observational (e.g., Ly$α$ strength, UV magnitude and spectral slope) and physical (e.g., stellar mass and star-formation rate) properties. We search for UV spectral features other than Ly$α$, such as higher-ionization nebular emission lines and absorption features. We successfully observe the OIII]1666 and CIII]909 collisionally excited emission lines and the HeII1640 recombination feature, as well as the resonant CIV1550 doublet either in emission or P-Cygni. We compare the observed spectral properties of the different mean spectra and find the emission lines to vary with the observational and physical properties of the LAEs. In particular, the mean spectra of LAEs with larger Ly$α$ equivalent widths, fainter UV magnitudes, bluer UV spectral slopes and lower stellar masses show the strongest nebular emission. The line ratios of these lines are similar to those measured in the spectra of local metal-poor galaxies, while their equivalent widths are weaker compared to the handful of extreme values detected in individual spectra of z>2 galaxies. This suggests that weak UV features are likely ubiquitous in high z, low-mass and faint LAEs. We publicly release the stacked spectra as they can serve as empirical templates for the design of future observations, such as those with the James Webb Space Telescope and the Extremely Large Telescope.

astro-ph.GA↗

arXiv2020

Dust Reverberation of 3C273: torus structure and lag -- luminosity relation

We monitored the z=0.158 quasar 3C273 between 2015 and 2019 in the optical (BVrz) and near-infrared (JHK) with the aim to perform dust reverberation mapping. Accounting for host galaxy and accretion disk contributions, we obtained pure dust light curves in JHK. Cross correlations between the V-band and the dust light curves yield an average rest-frame delay for the hot dust of tau_cent ~ 410 days. This is a factor 2 shorter than expected from the the dust ring radius R_x ~ 900 light days reported from interferometric studies. The dust covering factor (CF) is about 8%, much smaller than predicted from the half covering angle of 45 degree found for active galactic nuclei (AGN). We analyse the asymmetric shape of the correlation functions and explore whether an inclined bi-conical bowl-shaped dust torus geometry could bring these findings (tau_cent, R_x and CF) into a consistent picture. The hot varying dust emission originates from the edge of the bowl rim with a small covering angle 40 < theta < 45 degree, and we see only the near side of the bi-conus. Such a dust gloriole with R_x = 900 +/- 200 ld and an inclination i = 12 degree matches the data remarkably well. Comparing the results of 3C273 with literature for less luminous AGN, we find a lag-luminosity relation tau propto L^alpha with alpha between 0.33 and 0.40, flatter than the widely adopted relation with alpha = 0.5. We address several explanations for the new lag - luminosity relation.

astro-ph.GA↗

arXiv2019

A stellar census in globular clusters with MUSE: A spectral catalogue of emission-line sources

Globular clusters produce many exotic stars due to a much higher frequency of dynamical interactions in their dense stellar environments. Some of these objects were observed together with several hundred thousands other stars in our MUSE survey of 26 Galactic globular clusters. Assuming that at least a few exotic stars have exotic spectra, that means spectra that contain emission lines, we can use this large spectroscopic data set of over a million stellar spectra as a blind survey to detect stellar exotica in globular clusters. To detect emission lines in each spectrum, we model the expected shape of an emission line as a Gaussian curve. This template is used for matched filtering on the differences between each observed 1D spectrum and its fitted spectral model. The spectra with the most significant detections of H$α$ emission are checked visually and cross-matched with published catalogues. We find 156 stars with H$α$ emission, including several known cataclysmic variables (CV) and two new CVs, pulsating variable stars, eclipsing binary stars, the optical counterpart of a known black hole, several probable sub-subgiants and red stragglers, and 21 background emission-line galaxies. We find possible optical counterparts to 39 X-ray sources, as we detect H$α$ emission in several spectra of stars that are close to known positions of Chandra X-ray sources. This spectral catalogue can be used to supplement existing or future X-ray or radio observations with spectra of potential optical counterparts to classify the sources.

astro-ph.SR↗

arXiv2019

Discovery of an old nova remnant in the Galactic globular cluster M 22

A nova is a cataclysmic event on the surface of a white dwarf in a binary system that increases the overall brightness by several orders of magnitude. Although binary systems with a white dwarf are expected to be overabundant in globular clusters (GCs) compared to the Galaxy, only two novae from Galactic globular clusters have been observed. We present the discovery of an emission nebula in the Galactic globular cluster M 22 (NGC 6656) in observations made with the integral-field spectrograph MUSE. We extract the spectrum of the nebula and use the radial velocity determined from the emission lines to confirm that the nebula is part of NGC 6656. Emission-line ratios are used to determine the electron temperature and density. It is estimated to have a mass of 1 to $17 \times 10^{-5}$ solar masses. This mass and the emission-line ratios indicate that the nebula is a nova remnant. Its position coincides with the reported location of a 'guest star', an ancient Chinese term for transients, observed in May 48 BCE. With this discovery, this nova may be one of the oldest confirmed extrasolar events recorded in human history.

astro-ph.SR↗

arXiv2019

Exploring HeII$λ$1640 emission line properties at ${z\sim2-4}$

Deep optical spectroscopic surveys of galaxies provide us a unique opportunity to investigate rest-frame ultra-violet (UV) emission line properties of galaxies at ${z \sim 2-4.5}$. Here we combine VLT/MUSE Guaranteed Time Observations of the Hubble Deep Field South, Ultra Deep Field, COSMOS, and several quasar fields with other publicly available data from VLT/VIMOS and VLT/FORS2 to construct a catalogue of HeII$λ$1640 emitters at ${z\sim2}$. The deepest areas of our MUSE pointings reach a ${3σ}$ line flux limit of 3.1${\times}$10-19 erg/ s/ cm$^2$. After discarding broad line active galactic nuclei we find 13 HeII$λ$1640 detections from MUSE with a median MUV = $-20.1$ and 21 tentative HeII$λ$1640 detections from other public surveys. Excluding Ly$α$, all except two galaxies in our sample show at least one other rest-UV emission line, with CIII]$λ$1907,$λ$1909 being the most prominent. We use multi-wavelength data available in the Hubble legacy fields to derive basic galaxy properties of our sample via spectral energy distribution fitting techniques. Taking advantage of the high quality spectra obtained by MUSE (${\sim10 - 30}$h of exposure time per pointing), we use photo-ionisation models to study the rest-UV emission line diagnostics of the HeII$λ$1640 emitters. Line ratios of our sample can be reproduced by moderately sub-solar photo-ionisation models, however, we find that including effects of binary stars lead to degeneracies in most free parameters. Even after considering extra ionising photons produced by extreme sub-solar metallicity binary stellar models, photo-ionisation models are unable to reproduce rest-frame HeII$λ$1640 equivalent widths (${\sim}$ 0.2 - 10 A), thus additional mechanisms are necessary in models to match the observed HeII$λ$1640 properties.

astro-ph.GA↗

arXiv2018

The large and small scale properties of the intergalactic gas in the Slug Ly-alpha nebula revealed by MUSE HeII emission observations

With a projected size of about 450 kpc at z~2.3, the Slug Ly-alpha nebula is a rare laboratory to study, in emission, the properties of the intergalactic gas in the Cosmic Web. Since its discovery, the Slug has been the subject of several spectroscopic follow-ups to constrain the properties of the emitting gas. Here we report the results of a deep MUSE integral-field spectroscopic search for non-resonant, extended HeII1640 and metal emission. Extended HeII radiation is detected on scales of about 100 kpc, but only in some regions associated with the bright Ly-alpha emission and a continuum-detected source, implying large and abrupt variations in the line ratios across adjacent regions in projected space. The recent detection of associated H-alpha emission and similar abrupt variations in the Ly-alpha kinematics, strongly suggest that the HeII/Ly-alpha gradient is due to large variations in the physical distances between the associated quasar and these regions. This implies that the overall length of the emitting structure could extend to physical Mpc scales and be mostly oriented along our line of sight. At the same time, the relatively low HeII/Ly-alpha values suggest that the emitting gas has a broad density distribution that - if expressed in terms of a lognormal - implies dispersions as high as those expected in the interstellar medium of galaxies. These results strengthen the possibility that the density distribution of intergalactic gas at high-redshift is extremely clumpy and multiphase on scales below our current observational spatial resolution of a few physical kpc.

astro-ph.GA↗