Examinando por Autor "Riechers, D."

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    COLDz: Probing Cosmic Star Formation with Radio Free-Free Emission
    (IOP Publishing Ltd, 2022-01) Algera, H.; Hodge, J.; Riechers, D.; Leslie, S.; Smail, I.; Aravena, M.; Cunha, E.; Daddi, E.; Decarli, R.; Dickinson, M.; Gim, H.; Guaita, L.; Magnelli, B.; Murphy, E.; Pavesi, R.; Sargent, M.; Sharon, C.; Wagg, J.; Walter, F.; Yun, M.
    Radio free-free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum - being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys - the usage of free-free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free-free emission in typical galaxies at the peak of cosmic star formation. We find that z ∼ 0.5-3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65-90 GHz that is ∼1.5-2 times fainter than would be expected from a simple combination of free-free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free-free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free-free emission at 0.5 ≲ z ≲ 3, which are in good agreement with more established tracers at high redshift. In the future, deep multifrequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free-free emission as a tracer of high-redshift star formation.
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    Ítem
    Tomography of the environment of the COSMOS/AzTEC-3 submillimeter galaxy at z ∼ 5.3 revealed by Ly α and MUSE observations
    (EDP Sciences, 2022-04-01) Guaita, L.; Aravena, M.; Gurung-Lopez, S.; Cantalupo, S.; Marino, R.; Riechers, D.; Da Cunha, E.; Wagg, J.; Algera, H.S.B.; Dannerbauer, H.; Cox, P.
    Context. Submillimeter galaxies (SMGs) have been proposed as the progenitors of massive ellipticals in the local Universe. Mapping the neutral gas distribution and investigating the gas accretion toward the SMGs at high redshift can provide information on the way SMG environments can evolve into clusters at z = 0. Aims. In this work, we study the members of the protocluster around AzTEC-3, a submillimeter galaxy at z = 5.3. We use Lyα emission and its synergy with previous CO and [CII]158 μm observations. Methods. We analyzed the data from the Multi Unit Spectroscopic Explorer (MUSE) instrument in an area of 1.4×1.4 arcmin2 around AzTEC-3 and derived information on the Lyα line in emission. We compared the Lyα profile of various regions of the environment with the zELDA radiative transfer model, revealing the neutral gas distribution and kinematics. Results. We identified ten Lyα emitting sources, including two regions with extended emission: one embedding AzTEC-3 and LBG-3, which is a star-forming galaxy located 2′ (12 kpc) north of the SMG and another toward LBG-1, which is a star-forming galaxy located 15′ (90 kpc) to the southeast. The two regions extend for ∼27×38 kpc2 (∼170×240 ckpc2) and ∼20×20 kpc2 (∼125×125 ckpc2), respectively. The sources appear distributed in an elongated configuration of about 70′ (430 kpc) in extent. The number of sources confirms the overdensity around AzTEC-3. We study the MUSE spectra of the AzTEC-3+LBG-3 system and LBG-1 in detail. For the AzTEC-3+LBG-3 system, the Lyα emission appears redshifted and more spatially extended than the [CII] line emission. Similarly, the Lyα line spectrum is broader in velocity than [CII] for LBG-1. In the former spectrum, the Lyα emission is elongated to the north of LBG-3 and to the south of AzTEC-3, where a faint Lyα emitting galaxy is also located. The elongated structures could resemble tidal features due to the interaction of the two galaxies with AzTEC-3. Also, we find a bridge of gas, revealed by the Lyα emission between AzTEC-3 and LBG-3. The Lyα emission toward LBG-1 embeds its three components. The HI kinematics support the idea of a merger of the three components. Conclusions. Given the availability of CO and [CII] observations from previous campaigns, and the Lyα information from our MUSE dataset, we find evidence of starburst-driven phenomena and interactions around AzTEC-3. The stellar mass of the galaxies of the overdensity and the Lyα luminosity of the HI nebula associated with AzTEC-3 imply a dark matter halo of ∼1012 M· at z = 5.3. By comparing this with semi-analytical models, the dark matter halo mass indicates that the region could evolve into a cluster of 2×1013 M· by z = 2 and into a Fornax-type cluster at z = 0 with a typical mass of 2×1014âà €à † M·. © 2022 Authors