The Bimodal Absorption System Imaging Campaign (BASIC) I. A Dual Population of Low-metallicity Absorbers at z $&lt;1$

Berg, Michelle A.; Lehner, N.; Howk, J. Christopher; O’Meara, John M.; Schaye, Joop; Straka, Lorrie A.; Cooksey, Kathy L.; Tripp, Todd M.; Prochaska, J. Xavier; Oppenheimer, Benjamin D.; Johnson, Sean D.; Muzahid, Sowgat; Bordoloi, Rongmon; Werk, Jessica K.; Katz, Neal; Wendt, Martin; Peeples, Molly S.; Ribaudo, Joseph; Tumlinson, Jason

doi:10.48550/arxiv.2204.13229

Cited by 6 publications

(8 citation statements)

References 123 publications

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“…On the other hand, recent Very Large Telescope (VLT)/MUSE IFU observations of high-z LLSs also show that at least some of these absorbers may probe IGM filaments (Fumagalli et al 2016a;Lofthouse et al 2020). At z < 1, similar findings are found using Keck/KCWI and VLT/MUSE observations, where VMP pLLSs are found either in the CGM of galaxies or well outside (likely in the IGM), while metalenriched are always found in the CGM of galaxies (Berg et al 2022). With the FOGGIE simulations, we can explore the origins of these absorbers without observational constraints due to, e.g., the brightness limit of the galaxies.…”

Section: Insights From Foggie Simulationssupporting

confidence: 57%

“…Observationally, galaxy counterpart searches for two pristine LLSs with [X/H] < − 3.3 at z > 2 show no associated galaxies for one and a group of galaxies for the other one (Fumagalli et al 2016a). At z < 1, the recent BASIC galaxy survey of 19 pLLSs shows two populations for the VMP pLLSs, one associated with galaxy halos and another one well outside the virial radius of any galaxy, likely originating in the IGM (Berg et al 2022). It is therefore likely based on these observations and high-resolution simulations that a combination of these dual origins (IGM and cold inflow) can most likely explain the pristine and VMP absorbers.…”

Section: Pristine Gasmentioning

confidence: 84%

“…While pLLSs and LLSs have been found often in the CGM of galaxies at both low and high redshift (e.g., Lehner et al 2009Lehner et al , 2013Ribaudo et al 2011;Kacprzak et al 2012;Prochaska et al 2017b;Cooper et al 2021;Berg et al 2022), there is growing evidence that at least some of the pLLSs and LLSs with very low metallicities may probe the denser IGM (very low metallicity being [X/H]  −1.4 at z  1, Berg et al 2022; and [X/H]  −3 at 2  z  3.5, Fumagalli et al 2011aFumagalli et al , 2016aCrighton et al 2016;Lofthouse et al 2020). 13 Recent high-resolution zoom-in cosmological simulations also show that metal-poor ([X/H] < − 3) LLS-like absorbers can be found in the IGM far from any galaxies (Mandelker et al 2019(Mandelker et al , 2021.…”

Section: Introductionmentioning

confidence: 99%

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KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2 ≲ z ≲ 3.6

Lehner

Kopenhafer

O’Meara

et al. 2022

ApJ

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We present the KODIAQ-Z survey aimed to characterize the cool, photoionized gas at 2.2 ≲ z ≲ 3.6 in 202 H i-selected absorbers with 14.6 ≤ log N H I < 20 that probe the interface between galaxies and the intergalactic medium (IGM). We find that gas with 14.6 ≤ log N H I < 20 at 2.2 ≲ z ≲ 3.6 can be metal-rich (−1.6 ≲ [X/H] ≲ − 0.2) as seen in damped Lyα absorbers (DLAs); it can also be very metal-poor ([X/H] < − 2.4) or even pristine ([X/H] < − 3.8), which is not observed in DLAs but is common in the IGM. For 16 < log N H I < 20 absorbers, the frequency of pristine absorbers is about 1%–10%, while for 14.6 ≤ log N H I ≤ 16 absorbers it is 10%–20%, similar to the diffuse IGM. Supersolar gas is extremely rare (<1%) at these redshifts. The factor of several thousand spread from the lowest to highest metallicities and large metallicity variations (a factor of a few to >100) between absorbers separated by less than Δv < 500 km s−1 imply that the metals are poorly mixed in 14.6 ≤ log N H I < 20 gas. We show that these photoionized absorbers contribute to about 14% of the cosmic baryons and 45% of the cosmic metals at 2.2 ≲ z ≲ 3.6. We find that the mean metallicity increases with N H i , consistent with what is found in z < 1 gas. The metallicity of gas in this column density regime has increased by a factor ∼8 from 2.2 ≲ z ≲ 3.6 to z < 1, but the contribution of the 14.6 ≤ log N H I < 19 absorbers to the total metal budget of the universe at z < 1 is a quarter of that at 2.2 ≲ z ≲ 3.6. We show that FOGGIE cosmological zoom-in simulations have a similar evolution of [X/H] with N H i , which is not observed in lower-resolution simulations. In these simulations, very metal-poor absorbers with [X/H] < − 2.4 at z ∼ 2–3 are tracers of inflows, while higher-metallicity absorbers are a mixture of inflows and outflows.

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Section: Insights From Foggie Simulationssupporting

confidence: 57%

Section: Pristine Gasmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

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KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2 ≲ z ≲ 3.6

Lehner

Kopenhafer

O’Meara

et al. 2022

ApJ

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“…The bimodality is apparent in every metal line apart from Mg ii, and is broadly reproduced by the RF models. Populations of absorbers in the cool CGM of low redshift Lyman Limit Systems (LLSs) have also been observed to have bimodal metallicity distributions, with both metal-poor and metal-rich absorbers (albeit shifted to lower metallicities, Lehner et al 2013Lehner et al , 2018Lehner et al , 2019Wotta et al 2016Wotta et al , 2019Berg et al 2022), suggesting multiple origins for the cool CGM gas, although the metallicities of the observed metal-poor absorbers are much lower than that seen in Simba. In future work we will investigate the origin of the bimodal absorber metallicity distribution in Simba.…”

Section: Predictive Accuracymentioning

confidence: 99%

Mapping Circumgalactic Medium Observations to Theory Using Machine Learning

Appleby¹,

Davé²,

Sorini³

et al. 2023

Preprint

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We present a random forest framework for predicting circumgalactic medium (CGM) physical conditions from quasar absorption line observables, trained on a sample of Voigt profile-fit synthetic absorbers from the Simba cosmological simulation. Traditionally, extracting physical conditions from CGM absorber observations involves simplifying assumptions such as uniform single-phase clouds, but by using a cosmological simulation we bypass such assumptions to better capture the complex relationship between CGM observables and underlying gas conditions. We train random forest models on synthetic spectra for H i and selected metal lines around galaxies across a range of star formation rates, stellar masses, and impact parameters, to predict absorber overdensities, temperatures, and metallicities. The models reproduce the true values from Simba well, with transverse standard deviations of 0.2 − 0.3 dex in overdensity, 0.14 − 0.2 dex in temperature, and 0.16 − 0.2 dex in metallicity predicted from metal lines (not H i), across all ions. Examining the feature importance, the random forest indicates that the overdensity is most informed by the absorber column density, the temperature is driven by the line width, and the metallicity is most sensitive to the specific star formation rate. Alternatively examining feature importance by removing one observable at a time, the overdensity and metallicity appear to be more driven by the impact parameter. We introduce a normalising transform approach in order to ensure the scatter in the true physical conditions is accurately spanned by the network. The trained models are available online.

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“…Con-versely, Berg et al (2022) find an 80% chance of finding a massive galaxy nearby to any high-metallicity absorber. The CGM of M > 10 8 M galaxies is now wellestablished to be metal-enriched (Liang & Chen 2014;Bordoloi et al 2014;Prochaska et al 2017;Berg et al 2022), and to extend to at least 1 R vir , and very likely beyond it (Wakker & Savage 2009;Burchett et al 2015;Finn et al 2016;Wilde et al 2021;Borthakur 2022).…”

Section: Introductionmentioning

confidence: 98%

CGM$^2$ $+$ CASBaH: The Mass Dependence of H~I Ly$α$-Galaxy Clustering and the Extent of the CGM

Wilde¹,

Miville-Deschênes²,

Werk³

et al. 2023

Preprint

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We combine datasets from the CGM 2 and CASBaH surveys to model a transition point, R cross , between circumgalactic and intergalactic media (CGM and IGM, respectively). In total, our data consist of 7244 galaxies at z < 0.5 with precisely measured spectroscopic redshifts, all having impact parameters of 0.01 − 20 comoving Mpc from 28 QSO sightlines with high-resolution UV spectra that cover H I Lyα. Our best-fitting model is an exclusionary two-component model that combines a 3D absorber-galaxy cross correlation function with a simple Gaussian profile at inner radii to represent the CGM. By design, this model gives rise to a determination of R cross as a function of galaxy stellar mass, which can be interpreted as the boundary between the CGM and IGM. For galaxies with 10 8 ≤ M /M ≤ 10 10.5 , we find that R cross (M ) ≈ 2 ± 0.6R vir . Additionally, we find excellent agreement between R cross (M ) and the theoretically-determined splashback radius for galaxies in this mass range. Overall, our results favor models of galaxy evolution at z < 0.5 that distribute T ≈ 10 4 K gas to distances beyond the virial radius.

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The Bimodal Absorption System Imaging Campaign (BASIC) I. A Dual Population of Low-metallicity Absorbers at z $<1$

Cited by 6 publications

References 123 publications

KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2 ≲ z ≲ 3.6

KODIAQ-Z: Metals and Baryons in the Cool Intergalactic and Circumgalactic Gas at 2.2 ≲ z ≲ 3.6

Mapping Circumgalactic Medium Observations to Theory Using Machine Learning

CGM$^2$ $+$ CASBaH: The Mass Dependence of H~I Ly$α$-Galaxy Clustering and the Extent of the CGM

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