Extreme gas fractions in clumpy, turbulent disk galaxies at z~0.1

In this letter we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby Universe (z ~ 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted Halpha reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20-30% and depletion times of tdep ~ 0.5 Gyr (assuming a Milky Way-like CO conversion factor). These properties are unlike those expected for low- redshift galaxies of comparable specific star formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogues to the clumpy, turbulent disks, which are often found at high redshift.Comment: Accepted to ApJ Letter

Spatially resolved stellar, dust and gas properties of the post-interacting Whirlpool Galaxy system

Using infrared imaging from the Herschel Space Observatory, observed as part of the VNGS, we investigate the spatially resolved dust properties of the interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales of 1 kpc. Spectral energy distribution modelling of the new infrared images in combination with archival optical, near- through mid-infrared images confirms that both galaxies underwent a burst of star formation ~370-480 Myr ago and provides spatially resolved maps of the stellar and dust mass surface densities. The resulting average dust-to-stellar mass ratios are comparable to other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at log M(dust)/M(star)= -2.5+/-0.2 and NGC 5195 at log M(dust)/M(star)= -3.5+/-0.3. The dust-to-stellar mass ratio is constant across NGC 5194 suggesting the stellar and dust components are coupled. In contrast, the mass ratio increases with radius in NGC 5195 with decreasing stellar mass density. Archival mass surface density maps of the neutral and molecular hydrogen gas are also folded into our analysis. The gas-to-dust mass ratio, 94+/-17, is relatively constant across NGC 5194. Somewhat surprisingly, we find the dust in NGC 5195 is heated by a strong interstellar radiation field, over 20 times that of the ISRF in the Milky Way, resulting in relatively high characteristic dust temperatures (~30 K). This post-starburst galaxy contains a substantial amount of low-density molecular gas and displays a gas-to-dust ratio (73+/-35) similar to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such high temperatures as there is no star formation in the galaxy and its active galactic nucleus is 5-10 times less luminous than the one in NGC 5194, which exhibits only a modest enhancement in the amplitude of its ISRF.Comment: 26 pages, 24 figures, Accepted for publication in Ap

Cold Dust but Warm Gas in the Unusual Elliptical Galaxy NGC 4125

Data from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to its CO and Hi emission. Depending on the dust emissivity, the total dust mass is 2-5 x 10(6) M-circle dot. While the neutral gas-to-dust mass ratio is extremely low (= 10(4) K faster than the dust is evaporated. If galaxies like NGC 4125, where the far-infrared emission does not trace neutral gas in the usual manner, are common at higher redshift, this could have significant implications for our understanding of high redshift galaxies and galaxy evolution.Canadian Space AgencyNatural Sciences and Engineering Research Council of CanadaAgenzia Spaziale Italiana (ASI) I/005/11/0BMVIT (Austria)ESA-PRODEX (Belgium)CEA/CNES (France)DLR (Germany)ASI/INAF (Italy)CICYT/MCYT (Spain)CSA (Canada)NAOC (China)CEA, (France)CNES (France)CNRS (France)ASI (Italy)MCINN (Spain)SNSB (Sweden)STFC (UK)NASA (USA)National Aeronautics and Space AdministrationAstronom

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 an extremely high equivalent width (EW), EWLyα+N V,rest ≳921 Å, 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 nondetection in the HETDEX spectrum; thus the measured EW is a lower limit. The source is detected with significant emission lines (>7σ) at Lyα + N v λ1241, C iv λ1549, and a moderate emission line (∼4σ) at He ii λ1640 within the wavelength coverage of HETDEX (3500-5500 Å). The r-band magnitude is 24.57 from the Hyper Suprime-Cam-HETDEX joint survey with a detection limit of r = 25.12 at 5σ. The Lyα emission line spans a clearly resolved region of ∼10″ (85 kpc) in diameter. The Lyα line profile is strongly double peaked. The spectral decomposed blue gas and red gas Lyα emission are separated by ∼1.″2 (10.1 kpc) with a line-of-sight velocity offset of ∼1100 km s−1. This source is probably an obscured AGN with powerful winds

Searching for Supernovae in HETDEX Data Release 3

We have extracted 636 spectra taken at the positions of 583 transient sources from the third data release of the Hobby-Eberly Telescope Dark Energy eXperiment (HETDEX). The transients were discovered by the Zwicky Transient Facility (ZTF) during 2018-2022. The HETDEX spectra provide a potential means to obtain classifications for a large number of objects found by photometric surveys for free. We attempt to explore and classify the spectra by utilizing several template-matching techniques. We have identified two transient sources, ZTF20aatpoos = AT 2020fiz and ZTF19abdkelq, as supernova (SN) candidates. We classify AT 2020fiz as a Type IIP SN observed ∼10 days after explosion, and we propose ZTF19abdkelq as a likely Type Ia SN caught ∼40 days after maximum light. ZTF photometry of these two sources are consistent with their classifications as SNe. Beside these two objects, we have confirmed several ZTF transients as variable active galactic nuclei based on their spectral appearance, and determined the host galaxy types of several other ZTF transients

Using Dark Energy Explorers and Machine Learning to Enhance the Hobby-Eberly Telescope Dark Energy Experiment

We present analysis using a citizen science campaign to improve the cosmological measures from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the Hubble expansion rate, $H(z)$, and angular diameter distance, $D_A(z)$, at $z =$ 2.4, each to percent-level accuracy. This accuracy is determined primarily from the total number of detected Lyman-$\alpha$ emitters (LAEs), the false positive rate due to noise, and the contamination due to [O II] emitting galaxies. This paper presents the citizen science project, Dark Energy Explorers, with the goal of increasing the number of LAEs, decreasing the number of false positives due to noise and the [O II] galaxies. Initial analysis shows that citizen science is an efficient and effective tool for classification most accurately done by the human eye, especially in combination with unsupervised machine learning. Three aspects from the citizen science campaign that have the most impact are 1) identifying individual problems with detections, 2) providing a clean sample with 100% visual identification above a signal-to-noise cut, and 3) providing labels for machine learning efforts. Since the end of 2022, Dark Energy Explorers has collected over three and a half million classifications by 11,000 volunteers in over 85 different countries around the world. By incorporating the results of the Dark Energy Explorers we expect to improve the accuracy on the $D_A(z)$ and $H(z)$ parameters at $z =$ 2.4 by 10 - 30%. While the primary goal is to improve on HETDEX, Dark Energy Explorers has already proven to be a uniquely powerful tool for science advancement and increasing accessibility to science worldwide.Comment: 14 pages, 6 figures, accepted for publication in The Astrophysical Journa

Cosmological-scale Lyα Forest Absorption around Galaxies and AGNs Probed with the HETDEX and SDSS Spectroscopic Data

We present cosmological-scale three-dimensional neutral hydrogen (H i) tomographic maps at z = 2-3 over a total of 837 deg2 in two blank fields that are developed with Lyα forest absorptions of 14,736 background Sloan Digital Sky Survey (SDSS) quasars at z = 2.08-3.67. Using the tomographic maps, we investigate the large-scale (≳10 h −1 cMpc) average H i radial profiles and two-direction profiles of the line-of-sight (LOS) and transverse directions around galaxies and active galactic nuclei (AGNs) at z = 2-3 identified by the Hobby-Eberly Telescope Dark Energy eXperiment survey and SDSS, respectively. The peak of the H i radial profile around galaxies is lower than the one around AGNs, suggesting that the dark matter halos of galaxies are less massive on average than those of AGNs. The LOS profile of AGNs is narrower than the transverse profile, indicating the Kaiser effect. There exist weak absorption outskirts at ≳30 h −1 cMpc beyond H i structures of galaxies and AGNs found in the LOS profiles that can be explained by the H i gas at ≳30 h −1 cMpc falling toward the source position. Our findings indicate that the H i radial profile of AGNs has transitions from proximity zones (≲a few h −1 cMpc) to the H i structures (∼1-30 h −1 cMpc) and the weak absorption outskirts (≳30 h −1 cMpc). Although there is no significant dependence of AGN types (type 1 vs. type 2) on the H i profiles, the peaks of the radial profiles anticorrelate with AGN luminosities, suggesting that AGNs’ ionization effects are stronger than the gas mass differences

A multiwavelength analysis of the clumpy FIR-bright sources in M33

We present a multiwavelength study of a sample of far-infrared (FIR) sources detected on the Herschel broad-band maps of the nearby galaxy M33. We perform source photometry on the FIR maps as well as mid-infrared (MIR), Halpha, far-ultraviolet and integrated H I and CO line emission maps. By fitting MIR/FIR dust emission spectra, the source dust masses, temperatures and luminosities are inferred. The sources are classified based on their Halpha morphology (sub-structured versus not-substructured) and on whether they have a significant CO detection (S/N > 3sigma). We find that the sources have dust masses in the range 102-104 M&sun; and that they present significant differences in their inferred dust/star formation/gas parameters depending on their Halpha morphology and CO detection classification. The results suggests differences in the evolutionary states or in the number of embedded H II regions between the sub-samples. The source background-subtracted dust emission seems to be predominantly powered by local star formation, as indicated by a strong correlation between the dust luminosity and the dust-corrected Halpha luminosity and the fact that the extrapolated young stellar luminosity is high enough to account for the observed dust emission. Finally, we do not find a strong correlation between the dust-corrected Halpha luminosity and the dust mass of the sources, consistent with previous results on the breakdown of simple scaling relations at sub-kpc scales. However, the scatter in the relation is significantly reduced by correcting the Halpha luminosity for the age of the young stellar populations in the star-forming regions