arXiv subjects

Michael Rauch

Publications and source records attributed to Michael Rauch.

At least 55 records · Page 3Linked to original sources

arXiv2019

Probing IGM accretion onto faint Lyα emitters at z~2.8

(abridged) Observing the signature of accretion from the intergalactic medium (IGM) onto galaxies at z~3 requires the detection of faint (L<<L*) galaxies embedded in a filamentary matrix of low-density, metal-poor gas coherent over hundreds of kpc. We study the gaseous environment of three Lyman$α$ emitters (LAEs) at z=2.7-2.8, found to be aligned in projection with a background QSO over ~250 kpc along the slit of a long-slit spectrum. The lack of detection of the LAEs in deep continuum images and the low inferred Ly$α$ luminosities show the LAEs to be intrinsically faint, low-mass galaxies (L<0.1 L*, M_star< 0.1 M*). An echelle spectrum of the QSO reveals strong Ly-alpha absorption within $\pm200$ km/s from the LAEs. Our absorption line analysis leads to HI column densities in the range of log N(HI) =16-18. Associated absorption from ionic metal species CIV and SiIV constrains the gas metallicities to ~0.01 solar if the gas is optically thin, and possibly as low as ~0.001 solar if the gas is optically thick, assuming photoionization equilibrium. While the inferred metallicities are at least a factor of ten lower than expected metallicities in the interstellar medium (ISM) of these LAEs, they are consistent with the observed chemical enrichment level in the IGM at the same epoch. Total metal abundances and kinematic arguments suggest that these faint galaxies have not been able to affect the properties of their surrounding gas. The projected spatial alignment of the LAEs, together with the kinematic quiescence and correspondence between the LAEs and absorbing gas in velocity space suggests that these observations probe a possible filamentary structure. Taken together with the blue-dominant Ly$α$ emission line profile of one of the objects, the evidence suggests that the absorbing gas is part of an accretion stream of low-metallicity gas in the IGM.

astro-ph.GA↗

arXiv2019

Stress-testing the VBF approximation in multijet final states

We consider electro-weak Higgs plus three jets production at NLO QCD beyond strict VBF acceptance cuts. We investigate, for the first time, how accurate the VBF approximation is in these regions and within perturbative uncertainties, by a detailed comparison of full and approximate calculations. We find that a rapidity gap between the tagging jets guarantees a good approximation, while an invariant mass cut alone is not sufficient, which needs to be confronted with experimental choices. We also find that a significant part of the QCD corrections can be attributed to Higgs-Strahlungs-type topologies.

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arXiv2019

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

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, Σ_cool, by applying the estimated ionization fraction corrections to the observed HI column densities. The radial profile of Σ_cool is best-described by a projected Einasto profile of slope α=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.

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arXiv2018

SILVERRUSH. V. Census of Lya, [OIII]5007, Ha, and [CII]158um Line Emission with ~1000 LAEs at z=4.9-7.0 Revealed with Subaru/HSC

We investigate Lya, [OIII]5007, Ha, and [CII]158um emission from 1124 galaxies at z=4.9-7.0. Our sample is composed of 1092 Lya emitters (LAEs) at z=4.9, 5.7, 6.6, and 7.0 identified by Subaru/Hyper Suprime-Cam (HSC) narrowband surveys covered by Spitzer large area survey with Subaru/HSC (SPLASH) and 34 galaxies at z=5.148-7.508 with deep ALMA [CII]158um data in the literature. Fluxes of strong rest-frame optical lines of [OIII] and Ha (Hb) are constrained by significant excesses found in the SPLASH 3.6 and 4.5um photometry. At z=4.9, we find that the rest-frame Ha equivalent width and the Lya escape fraction f_Lya positively correlate with the rest-frame Lya equivalent width EW^0_Lya. The f_Lya-EW^0_Lya correlation is similarly found at z~0-2, suggesting no evolution of the correlation over z~0-5. The typical ionizing photon production efficiency of LAEs is logxi_ion/[Hz erg^-1]~25.5 significantly (60-100%) higher than those of LBGs at a given UV magnitude. At z=5.7-7.0, there exists an interesting turn-over trend that the [OIII]/Ha flux ratio increases in EW^0_Lya~0-30 A, and then decreases out to EW^0_Lya~130 A. We also identify an anti-correlation between a [CII] luminosity to star-formation rate ratio (L_[CII]/SFR) and EW^0_Lya at the >99% confidence level. We carefully investigate physical origins of the correlations with stellar-synthesis and photoionization models, and find that a simple anti-correlation between EW_Lya^0 and metallicity explains self-consistently all of the correlations of Lya, Ha, [OIII]/Ha, and [CII] identified in our study, indicating detections of metal-poor (~0.03 Zo) galaxies with EW^0_Lya~200 A.

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arXiv2017

Higgs Factories: Higgs-Strahlung versus W-Fusion

Higgs factories will be able to measure Higgs properties, and in particular Higgs couplings with high precision. In a follow-up to an earlier analysis we study the impact of the Higgs-strahlung and vector boson fusion processes on the precision of the couplings determination. Provided theoretical uncertainties can be controlled, future Higgs factories will be able to measure Higgs couplings at the sub-percent level. In spite of their different strengths, base-line circular and linear designs can expect a surprisingly similar performance.

hep-ph↗

arXiv2017

SILVERRUSH. III. Deep Optical and Near-Infrared Spectroscopy for Lya and UV-Nebular Lines of Bright Lya Emitters at z=6-7

We present Lya and UV-nebular emission line properties of bright Lya emitters (LAEs) at z=6-7 with a luminosity of log L_Lya/[erg s-1] = 43-44 identified in the 21-deg2 area of the SILVERRUSH early sample developed with the Subaru Hyper Suprime-Cam (HSC) survey data. Our optical spectroscopy newly confirm 21 bright LAEs with clear Lya emission, and contribute to make a spectroscopic sample of 96 LAEs at z=6-7 in SILVERRUSH. From the spectroscopic sample, we select 7 remarkable LAEs as bright as Himiko and CR7 objects, and perform deep Keck/MOSFIRE and Subaru/nuMOIRCS near-infrared spectroscopy reaching the 3sigma-flux limit of ~ 2x10^{-18} erg s-1 for the UV-nebular emission lines of He II1640, C IV1548,1550, and O III]1661,1666. Except for one tentative detection of C IV, we find no strong UV-nebular lines down to the flux limit, placing the upper limits of the rest-frame equivalent widths (EW_0) of ~2-4 A for He II, C IV, and O III] lines. Here we also investigate the VLT/X-SHOOTER spectrum of CR7 whose 6 sigma detection of He II is claimed by Sobral et al. Although two individuals and the ESO-archive service carefully re-analyze the X-SHOOTER data that are used in the study of Sobral et al., no He II signal of CR7 is detected, supportive of weak UV-nebular lines of the bright LAEs even for CR7. Spectral properties of these bright LAEs are thus clearly different from those of faint dropouts at z~7 that have strong UV-nebular lines shown in the various studies. Comparing these bright LAEs and the faint dropouts, we find anti-correlations between the UV-nebular line EW_0 and UV-continuum luminosity, which are similar to those found at z~2-3.

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arXiv2017

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

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.

astro-ph.GA↗

arXiv2017

Great Optically Luminous Dropout Research Using Subaru HSC (GOLDRUSH). I. UV Luminosity Functions at $z \sim 4-7$ Derived with the Half-Million Dropouts on the 100 deg$^2$ Sky

We study the UV luminosity functions (LFs) at $z\sim 4$, $5$, $6,$ and $7$ based on the deep large-area optical images taken by the Hyper Suprime-Cam (HSC) Subaru strategic program (SSP). On the 100 deg$^2$ sky of the HSC SSP data available to date, we make enormous samples consisting of a total of 579,565 dropout candidates at $z\sim 4-7$ by the standard color selection technique, 358 out of which are spectroscopically confirmed by our follow-up spectroscopy and other studies. We obtain UV LFs at $z \sim 4-7$ that span a very wide UV luminosity range of $\sim 0.002 - 100 \, L_{\rm UV}^\ast$ ($-26 < M_{\rm UV} < -14$ mag) by combining LFs from our program and the ultra-deep Hubble Space Telescope legacy surveys. We derive three parameters of the best-fit Schechter function, $ϕ^\ast$, $M_{\rm UV}^\ast$, and $α$, of the UV LFs in the magnitude range where the AGN contribution is negligible, and find that $α$ and $ϕ^\ast$ decrease from $z\sim 4$ to $7$ with no significant evolution of $M_{\rm UV}^\ast$. Because our HSC SSP data bridge the LFs of galaxies and AGNs with great statistical accuracy, we carefully investigate the bright end of the galaxy UV LFs that are estimated by the subtraction of the AGN contribution either aided with spectroscopy or the best-fit AGN UV LFs. We find that the bright end of the galaxy UV LFs cannot be explained by the Schechter function fits at $> 2 σ$ significance, and require either double power-law functions or modified Schechter functions that consider a magnification bias due to gravitational lensing.

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arXiv2017

Gauging Metallicity of Diffuse Gas Under An Uncertain Ionizing Radiation Field

Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements, because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically-enriched outflows or in more chemically-pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities . Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.

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arXiv2017

Jet clustering dependence of VBF Higgs production

Precise predictions for Higgs production via vector-boson fusion play an important role when testing the properties of the Higgs boson and probing new-physics effects. While the inclusive cross section changes little when including NNLO and N3LO QCD corrections, a differential NNLO calculation with typical VBF cuts shows large corrections of up to 10% in distributions. In this article, we investigate the dependence of the differential NNLO QCD calculation on the jet definition. Starting from the known results at a fixed jet clustering choice, we use the electroweak H+3 jets production cross section at NLO precision to derive NNLO results for H+2 jets production for other jet definitions. We find that larger clustering radii significantly reduce the impact of NNLO corrections. The sizable NNLO corrections for distributions are largely caused by the broader energy flow inside jets at NNLO and are to be expected generally for processes with jets at LO.

hep-ph↗

arXiv2017

Herwig 7.1 Release Note

A new release of the Monte Carlo event generator Herwig (version 7.1) is now available. This version introduces a number of improvements, notably: multi-jet merging with the dipole shower at LO and NLO QCD; a new model for soft interactions and diffraction; improvements to mass effects and top decays in the dipole shower, as well as a new tune of the hadronisation parameters.

hep-ph↗

arXiv2016

On the radial profile of gas-phase Fe/α ratio around distant galaxies

This paper presents a study of the chemical compositions in cool gas around a sample of 27 intermediate-redshift galaxies. The sample comprises 13 massive quiescent galaxies at z=0.40-0.73 probed by QSO sightlines at projected distances d=3-400 kpc, and 14 star-forming galaxies at z=0.10-1.24 probed by QSO sightlines at d=8-163 kpc. The main goal of this study is to examine the radial profiles of the gas-phase Fe/α ratio in galaxy halos based on the observed Fe II to Mg II column density ratios. Because Mg+ and Fe+ share similar ionization potentials, the relative ionization correction is small in moderately ionized gas and the observed ionic abundance ratio N(Fe II)/N(Mg II) places a lower limit to the underlying (Fe/Mg) elemental abundance ratio. For quiescent galaxies, a median and dispersion of log =-0.06+/-0.15 is found at d<~60 kpc, which declines to log <-0.3 at d>~100 kpc. On the other hand, star-forming galaxies exhibit log =-0.25+/-0.21 at d<~60 kpc and log =-0.9+/-0.4 at larger distances. Including possible differential dust depletion or ionization correction would only increase the inferred (Fe/Mg) ratio. The observed N(FeII)/N(Mg II) implies super-solar Fe/α ratios in the inner halo of quiescent galaxies. An enhanced Fe abundance indicates a substantial contribution by Type Ia supernovae in the chemical enrichment, which is at least comparable to what is observed in the solar neighborhood or in intracluster media but differs from young star-forming regions. In the outer halos of quiescent galaxies and in halos around star-forming galaxies, however, the observed N(Fe II)/N(Mg II) is consistent with an α-element enhanced enrichment pattern, suggesting a core-collapse supernovae dominated enrichment history.

astro-ph.GA↗

arXiv2016

Ly$α$ Emitters with Very Large Ly$α$ Equivalent Widths, EW$_{\rm 0}$(Ly$α$) $\simeq 200-400$ Å, at $z\sim 2$

We present physical properties of spectroscopically confirmed Ly$α$ emitters (LAEs) with very large rest-frame Ly$α$ equivalent widths EW$_{\rm 0}$(Ly$α$). Although the definition of large EW$_{\rm 0}$(Ly$α$) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from $\sim 3000$ LAEs at $z\sim 2$ with reliable measurements of EW$_{\rm 0}$ (Ly$α$) $\simeq 200-400$ Å given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW$_{\rm 0}$(Ly$α$) LAEs do not have signatures of AGN, but notably small stellar masses of $M_{\rm *} = 10^{7-8}$ $M_{\rm \odot}$ and high specific star-formation rates (star formation rate per unit galaxy stellar mass) of $\sim 100$ Gyr$^{-1}$. These LAEs are characterized by the median values of $L({\rm Lyα})=3.7\times 10^{42}$ erg s$^{-1}$ and $M_{\rm UV}=-18.0$ as well as the blue UV continuum slope of $β= -2.5\pm0.2$ and the low dust extinction $E(B-V)_{\rm *} = 0.02^{+0.04}_{-0.02}$, which indicate a high median Ly$α$ escape fraction of $f_{\rm esc}^{\rm Lyα}=0.68\pm0.30$. This large $f_{\rm esc}^{\rm Lyα}$ value is explained by the low {\sc Hi} column density in the ISM that is consistent with FWHM of the Ly$α$ line, ${\rm FWHM (Lyα)}=212\pm32$ km s$^{-1}$, significantly narrower than those of small EW$_{\rm 0}$(Ly$α$) LAEs. Based on the stellar evolution models, our observational constraints of the large EW$_{\rm 0}$ (Ly$α$), the small $β$, and the rest-frame He{\sc ii} equivalent width imply that at least a half of our large EW$_{\rm 0}$(Ly$α$) LAEs would have young stellar ages of $\lesssim 20$ Myr and very low metallicities of $Z<0.02 Z_\odot$ regardless of the star-formation history.

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arXiv2016

Vector-Boson Fusion and Vector-Boson Scattering

Vector-boson fusion and vector-boson scattering are an important class of processes for the Large Hadron Collider at CERN. It is characterized by two high-energetic jets in the forward regions of the detector and reduced jet activity in the central region. The higher center-of-mass energy during the current and subsequent runs strongly boosts the sensitivity in these processes and allows to test the predictions of the Standard Model to a high precision. In this review, we first present the main phenomenological features of vector-boson fusion and scattering processes. Then we discuss the effects of higher-order corrections, which are available at NLO QCD for all processes and up to N3LO QCD and NLO electro-weak for VBF-H production. An additional refinement is the addition of parton-shower effects, where recently a lot of progress has been made. The appearance of triple and quartic gauge vertices in the production processes enables us to probe anomalous gauge couplings. We introduce and compare the different parametrizations used in the literature and also discuss the issue of unitarity violation and common unitarization procedures. Finally, we give a short overview of current and possible future experimental searches.

hep-ph↗

arXiv2016

Learning from the New Higgs-like Scalar before It Vanishes

Motivated by a di-photon anomaly observed by ATLAS and CMS we develop an SFitter analysis for a combined electroweak-Higgs sector, and a scalar portal at the LHC. The theoretical description is based on the linear effective Lagrangian for the Higgs and gauge fields, combined with an additional singlet scalar. The key feature is the extraction of reliable information on the portal structure of the combined scalar potential. For the specific di-photon anomaly we find that the new state might well form such a Higgs portal. To obtain more conclusive results we define and test the connection of the Wilson coefficients in the Higgs and heavy scalar sectors, as suggested by a portal setup.

hep-ph↗

arXiv2016

Parton-shower Effects in Vector-Boson-Fusion Processes

We investigate the effects of combining next-to-leading order QCD results with parton-shower effects in $W^+W^-jj$ production via vector-boson fusion including leptonic decays. Using the Herwig 7 framework interfaced to VBFNLO 3, we compare the predictions obtained from the angular-ordered and dipole-based parton shower algorithms combined with subtractive, MC@NLO-type, and multiplicative, Powheg-type, matching. A consistent treatment of renormalisation and factorisation scale variations in the hard process and the parton shower allows to assign more reliable theory uncertainty predictions to key distributions like the central rapidity gap.

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arXiv2016

Parton Shower Matching Systematics in Vector-Boson-Fusion WW Production

We perform a detailed analysis of next-to-leading order plus parton-shower matching in vector-boson-fusion WW production including leptonic decays. The study is performed in the Herwig 7 framework interfaced to VBFNLO 3, using the angular-ordered and dipole-based parton-shower algorithms combined with the subtractive and multiplicative matching algorithms.

hep-ph↗

arXiv2016

The Gauge-Higgs Legacy of the LHC Run I

The effective Lagrangian expansion provides a framework to study effects of new physics at the electroweak scale. To make full use of LHC data in constraining higher-dimensional operators we need to include both the Higgs and the electroweak gauge sector in our study. We first present an analysis of the relevant di-boson production LHC results to update constraints on triple gauge boson couplings. Our bounds are several times stronger than those obtained from LEP data. Next, we show how in combination with Higgs measurements the triple gauge vertices lead to a significant improvement in the entire set of operators, including operators describing Higgs couplings.

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