Calibrating Galaxy Redshifts Using Absorption by the Surrounding Intergalactic Medium

Abstract

Rest-frame UV spectral lines of star-forming galaxies are systematically offset from the galaxies' systemic redshifts, probably because of large-scale outflows. We calibrate galaxy redshifts measured from rest-frame UV lines by utilizing the fact that the mean HI Ly-alpha absorption profiles around the galaxies, as seen in spectra of background objects, must be symmetric with respect to the true galaxy redshifts if the galaxies are oriented randomly with respect to the lines of sight to the background objects. We use 15 QSOs at z~2.5-3 and more than 600 foreground galaxies with spectroscopic redshifts at z~1.9-2.5. All galaxies are within 2 Mpc proper from the lines of sight to the background QSOs. We find that LyA emission and ISM absorption redshifts require systematic shifts of v_LyA=-295(+35)(-35) km/s and v_ISM=145(+70)(-35) km/s. Assuming a Gaussian distribution, we put 1-sigma upper limits on possible random redshift offsets of <220 km/s for LyA and <420 km/s for ISM redshifts. For the small subset (<10%) of galaxies for which near-IR spectra have been obtained, we can compare our results to direct measurements based on nebular emission lines which we confirm to mark the systemic redshifts. While our v_ISM agrees with the direct measurements, our v_LyA is significantly smaller. However, when we apply our method to the near-IR subsample which is characterized by slightly different selection effects, the best-fit velocity offset comes into agreement with the direct measurement. This confirms the validity of our approach, and implies that no single number appropriately describes the whole population of galaxies, in line with the observation that the line offset depends on galaxy spectral morphology. This method provides accurate redshift calibrations and will enable studies of circumgalactic matter around galaxies for which rest-frame optical observations are not available.

7 pages, 3 figures, accepted for publication in MNRAS

References in corpus (8)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• The MUSE second-generation VLT instrument
• The Stellar, Gas and Dynamical Masses of Star-Forming Galaxies at z~2
• 3D Lyman-alpha radiation transfer. I. Understanding Lyman-alpha line profile morphologies
• 3D Lyman-alpha radiation transfer. III. Constraints on gas and stellar properties of z~3 Lyman break galaxies (LBG) and implications for high-z LBGs and Lyman-alpha emitters(LAEs)
• 3D Lya radiation transfer. II. Fitting the Lyman break galaxy MS 1512-cB58 and implications for Lya emission in high-z starbursts
• Cross correlation of Lyman-alpha absorbers with gas-rich galaxies
• The association between gas and galaxies II: The 2-point correlation function

Cited by in corpus (47)

• The Gaseous Environment of High-z Galaxies: Precision Measurements of Neutral Hydrogen in the Circumgalactic Medium of z ~ 2-3 Galaxies in the Keck Baryonic Structure Survey
• Metal-line absorption around $z\approx$2.4 star-forming galaxies in the Keck Baryonic Structure Survey
• Properties of gas in and around galaxy haloes
• The Spectroscopic Properties of Lyα-Emitters at z $\approx$ 2.7: Escaping Gas and Photons from Faint Galaxies
• Cold accretion flows and the nature of high column density HI absorption at redshift 3
• The Detectability of Lyman Alpha Emission from Galaxies during the Epoch of Reionization
• Recovering the systemic redshift of galaxies from their Lyman-alpha line profile
• Metal-enriched, sub-kiloparsec gas clumps in the circumgalactic medium of a faint z = 2.5 galaxy
• Gas Motion Study of Lya Emitters at z~2 Using UV and Optical Spectral Lines
• The MUSE Hubble Ultra Deep Field surveys: Data release II
• First Data Release of the COSMOS Lyman-Alpha Mapping And Tomography Observations: 3D Lyman-$\alpha$ Forest Tomography at 2.05 < z < 2.55
• The MUSE-Wide Survey: A first catalogue of 831 emission line galaxies
• A Close Comparison between Observed and Modeled Lyα Lines for z ~ 2.2 Lyman Alpha Emitters
• Neutral hydrogen optical depth near star-forming galaxies at z~2.4 in the Keck Baryonic Structure Survey
• Shadow of a Colossus: A z=2.45 Galaxy Protocluster Detected in 3D Ly-a Forest Tomographic Mapping of the COSMOS Field
• MUSE searches for galaxies near very metal-poor gas clouds at z~3: new constraints for cold accretion models
• The MUSE Hubble Ultra Deep Field Survey X. Ly$\alpha$ Equivalent Widths at $2.9<z<6.6$
• The MUSE Extremely Deep Field: the Cosmic Web in Emission at High Redshift
• A comparison of observed and simulated absorption from HI, CIV, and SiIV around $z\approx 2$ star-forming galaxies suggests redshift-space distortions are due to inflows
• Metal-Poor, Cool Gas in the Circumgalactic Medium of a z = 2.4 Star-Forming Galaxy: Direct Evidence for Cold Accretion?
• MUSEQuBES: Calibrating the redshifts of Ly α emitters using stacked circumgalactic medium absorption profiles
• Dissecting the Gaseous Halos of z~2 Damped Ly$\alpha$ Systems with Close Quasar Pairs
• The ALMA Spectroscopic Survey in the HUDF: Nature and physical properties of gas-mass selected galaxies using MUSE spectroscopy
• MUSE Analysis of Gas around Galaxies (MAGG) -- I: Survey design and the environment of a near pristine gas cloud at z~3.5
• On the connection between the intergalactic medium and galaxies: The HI-galaxy cross-correlation at z < 1
• Witnessing galaxy assembly in an extended z~3 structure
• The filling factor of intergalactic metals at redshift z=3
• Linking gas and galaxies at high redshift: MUSE surveys the environments of six damped Lyman alpha galaxies at z~3
• Detection of hot, metal-enriched outflowing gas around $z\approx$2.3 star-forming galaxies in the Keck Baryonic Structure Survey
• MUSEQuBES: Characterizing the circumgalactic medium of redshift $\approx 3.3$ Ly$\alpha$ emitters
• Deciphering Lyman $\alpha$ blob 1 with deep MUSE observations
• A measurement of galaxy halo mass from the surrounding HI Lyα absorption
• Environmental Dependence of Galactic Properties Traced by Ly$\alpha$ Forest Absorption: Diversity among Galaxy Populations
• Recovery and analysis of rest-frame UV emission lines in 2052 galaxies observed with MUSE at $1.5<z<6.4$
• MUSE Analysis of Gas around Galaxies (MAGG) -- V: Linking ionized gas traced by CIV and SiIV absorbers to Ly$\alpha$ emitting galaxies at $z\approx 3.0-4.5$
• The CGM at Cosmic Noon with KCWI: Outflows from a Star-forming Galaxy at z=2.071
• A population of ultraviolet-dim protoclusters detected in absorption
• The MUSE-Wide survey: Detection of a clustering signal from Lyman-α-emitters at 3<z<6
• LineStacker: A spectral line stacking tool for interferometric data
• Catch Me if You Can: Biased Distribution of Ly$\alpha$-emitting Galaxies according to the Viewing Direction
• Constraining the cosmic UV background at z>3 with MUSE Lyman-α emission observations
• The relationship between gas and galaxies at z<1 using the Q0107 quasar triplet
• Connection Between Galaxies and HI in the Circumgalactic and Intergalactic Media: Variation According to Galaxy Stellar Mass and Star-formation Activity
• Star-forming Galactic Contrails at z=3.2 as a Source of Metal Enrichment and Ionizing Radiation
• Improving photometric redshifts with Ly$\alpha$ tomography
• The Lyman-$\alpha$ Forest from LBGs: First 3D Correlation Measurement with DESI and Prospects for Cosmology
• The AGEL Survey: Spectroscopic Confirmation of Strong Gravitational Lenses in the DES and DECaLS Fields Selected Using Convolutional Neural Networks