We present Keck/DEIMOS spectroscopy of Segue 1, an ultra-low-luminosity (M_V_=-1.5^+0.6^_-0.8_) Milky Way satellite companion. While the combined size and luminosity of Segue 1 are consistent with either a globular cluster or a dwarf galaxy, we present spectroscopic evidence that this object is a dark matter-dominated dwarf galaxy. We identify 24 stars as members of Segue 1 with a mean heliocentric recession velocity of 206+/-1.3km/s. Although Segue 1 spatially overlaps the leading arm of the Sagittarius stream, its velocity is 100km/s different from that predicted for recent Sagittarius tidal debris at this position. Using spectral synthesis modeling, we derive a metallicity for the single red giant branch star in our sample of [Fe/H]=-3.3+/-0.2dex. We conclude that Segue 1 is the least luminous of the ultra-faint galaxies recently discovered around the Milky Way, and is thus the least-luminous known galaxy.
In this paper, we present high-resolution optical spectra and optical classifications from our large sample of 285 warm infrared galaxies 10^8^<L_IR_<10^12.5^L_{sun}_. We have classified these galaxies using new theoretical lines on the standard optical diagnostic diagrams. We use a theoretical extreme mixing line between the starburst and AGN regions to classify LINER galaxies and we define a theoretical boundary separating AGNs from starbursts. We find that many galaxies previously classified as LINERs appear to lie on a mixing sequence between starburst and AGN type galaxies.
We report the results of long-slit spectroscopy at position angles 68{deg}, 131{deg}, and 164{deg} for the minor-merger NGC 4194, a luminous infrared starburst galaxy. The mass within 1.2kpc of the dynamical center is estimated to be 4.8*109 to 1.7*1010 M{sun}, depending on the assumed inclination to the plane of the sky. The star formation rate (SFR) in the areas sampled is 8 M{sun}/yr. The metallicity, log(O/H)+12, ranges from ~8.8 to >9.0 in regions of significant star formation, suggesting that the metallicity has been enhanced by the current star formation. The star-forming regions range in age from 5 to 9Myr, with the youngest ages occurring in the regions of high SFR. Electron temperatures and the location of the spectra in emission line diagnostic diagrams suggest the presence of shock waves, presumably due to the presence of supernovae, winds from massive stars, and/or collisions of clouds due to the merger. The presence of massive stars and supernovae is consistent with the ages determined for the star-forming regions. The ages of the continua produced by the stellar population are estimated to range from 10Myr to 5Gyr. Much of the stellar population represented in the continua was probably formed before the merger and represents the progenitor galaxies.
It has been shown that the ultra-faint dwarf galaxy Eridanus 2 may host a stellar cluster in its centre. If this cluster is shown to exist, it can be used to set constraints on the mass and abundance of massive astrophysical compact halo objects (MACHOs) as a form of dark matter. Previous research has shown promising expectations in the mass range of 10-100M_{sun}_, but lacked spectroscopic measurements of the cluster. We aim to provide spectroscopic evidence regarding the nature of the putative star cluster in Eridanus 2 and to place constraints on MACHOs as a constituent of dark matter. We present spectroscopic observations of the central square arcminute of Eridanus 2 from MUSE-Faint, a survey of ultrafaint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. We derived line-of-sight velocities for possible member stars of the putative cluster and for stars in the centre of Eridanus 2. We discuss the existence of the cluster and determine new constraints for MACHOs using the Fokker-Planck diffusion approximation. Out of 182 extracted spectra, we identify 26 member stars of Eridanus 2, seven of which are possible cluster members. We find intrinsic mean line-of-sight velocities of 79.7^+3.1^_3.8_km/s and 76.0^+3.2^_3.7_km/s for the cluster and the bulk of Eridanus 2, respectively, as well as intrinsic velocity dispersions of <7.6km/s (68-% upper limit) and 10.3^+3.9^_3.2_km/s, respectively. This indicates that the cluster most likely exists as a distinct dynamical population hosted by Eridanus 2 and that it does not have a surplus of dark matter over the background distribution. Among the member stars in the bulk of Eridanus 2, we find possible carbon stars, alluding to the existence of an intermediate-age population.We derived constraints on the fraction of dark matter that can consist of MACHOs with a given mass between 1-10^5^M_{sun}_. For dark matter consisting purely of MACHOs, the mass of the MACHOs must be less than 7.6M_{sun}_ and 44M_{sun}_ at a 68- and 95-% confidence level, respectively.
We investigate the types of nuclear environments that produce OH megamasers (OHMs) with a study of the optical spectra of 40 OHM host galaxies and a control sample of 30 non-masing (ultra)luminous infrared galaxies ([U]LIRGs). The optical spectrophotometry provides spatially resolved spectra of multiple nuclei in a few of these merging systems. Of the 40 OHMs classified, 33% are starbursts, 42% are LINERs, and 25% are Seyfert 2 galaxies; the classification of the non-masing control sample is similar.
Spectroscopy of UltraStrong Emission Line galaxies
Short Name:
J/ApJ/668/853
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe the results of a narrowband search for ultrastrong emission line galaxies (USELs) with EW(H{beta})>=30{AA}. A total of 542 candidate galaxies are found in a one-half square degree survey using two ~120{AA} filters centered at 8150 and 9140{AA} with Subaru SuprimeCam. Follow-up spectroscopy for randomly selected objects in the candidate sample with Keck II DEIMOS shows that they consist of [OIII] {lambda}5007-, [OII] {lambda}3727-, and H{alpha}-selected strong emission line galaxies at intermediate redshift (z<1) and Ly{alpha}-emitting galaxies at high redshift (z>>5).
We present spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way (MW), Ursa Major II, and Coma Berenices obtained with the Keck/High Resolution Echelle Spectrometer (HIRES). These observations include the first high-resolution spectroscopic observations of extremely metal-poor ([Fe/H]<-3.0) stars not belonging to the MW halo field star population. We obtain abundance measurements and upper limits for 26 elements between carbon and europium. The entire sample of stars spans a range of -3.2<[Fe/H]<-2.3, and we confirm that each galaxy contains a large intrinsic spread of Fe abundances. A comparison with MW halo stars of similar metallicities reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and the MW halo for the light, {alpha}, and iron-peak elements (C to Zn). The abundances of neutron-capture elements (Sr to Eu) in the ultra-faint dwarf galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H]>~-3.0. Not only are our results broadly consistent with a galaxy formation model that predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]>-2.5) of the MW halo, but they also suggest that the faintest known dwarfs may be the primary contributors to the metal-poor end of the MW halo metallicity distribution.
We present the first results of our optical spectroscopy program aimed to provide redshifts and identifications for the X-ray sources in the Extended Chandra Deep Field South. A total of 339 sources were targeted using the IMACS spectrograph at the Magellan telescopes and the VIMOS spectrograph at the VLT. We measured redshifts for 186 X-ray sources, including archival data and a literature search. We find that the active galactic nucleus (AGN) host galaxies have on average redder rest-frame optical colors than nonactive galaxies, and that they live mostly in the "green valley". The dependence of the fraction of AGNs that are obscured on both luminosity and redshift is confirmed at high significance and the observed AGN spatial density is compared with the expectations from existing luminosity functions. These AGNs show a significant difference in the mid-IR to X-ray flux ratio for obscured and unobscured AGNs, which can be explained by the effects of dust self-absorption on the former. This difference is larger for lower luminosity sources, which is consistent with the dust opening angle depending on AGN luminosity.
We present Keck-MOSFIRE H and K spectra for a sample of 24 candidate quiescent galaxies at 3<z<4, identified from their rest-frame UVJ colors and photometric redshifts in the ZFOURGE and 3DHST surveys. With median integration times of one hour in H and five in K, we obtain spectroscopic redshifts for half of the sample, using either Balmer absorption lines or nebular emission lines. We confirm the high accuracy of the photometric redshifts for this spectroscopically-confirmed sample, with a median |Zphot-Zspec|/(1+Zspec) of 1.2%. Two galaxies turn out to be dusty H{alpha} emitters at lower redshifts (z<2.5), and these are the only two detected in the sub-mm with ALMA. High equivalent-width [OIII] emission is observed in two galaxies, contributing up to 30% of the K-band flux and mimicking the UVJ colors of an old stellar population. This implies a failure rate of only 20% for the UVJ selection at these redshifts. Lastly, Balmer absorption features are identified in four galaxies, among the brightest of the sample, confirming the absence of OB stars. We then modeled the spectra and photometry of all quiescent galaxies with a wide range of star-formation histories. We find specific star-formation rates (sSFR) lower than 0.15Gyr^-1^ (a factor of ten below the main sequence) for all but one galaxy, and lower than 0.01Gyr^-1^ for half of the sample. These values are consistent with the observed H{beta} and [OII] luminosities, and the ALMA non-detections. The implied formation histories reveal that these galaxies have quenched on average 300Myr prior to being observed, between z=3.5 and 5, and that half of their stars were formed by z~5.5 with a mean SFR~300M_{sun}_/yr. We finally compared the UVJ selection to a selection based instead on the sSFR, as measured from the photometry. We find that galaxies a factor of ten below the main sequence are 40% more numerous than UVJ-selected quiescent galaxies, implying that the UVJ selection is pure but incomplete. Current models fail at reproducing our observations, and underestimate either the number density of quiescent galaxies by more than an order of magnitude, or the duration of their quiescence by a factor two. Overall, these results confirm the existence of an unexpected population of quiescent galaxies at z>3, and offer the first insights on their formation histories.
We present a comprehensive catalog of high signal-to-noise ratio spectra obtained with DEIMOS on the Keck II telescope for a sample of F850LP<22.43mag(AB) field spheroidal (E+S0 galaxies; 165) and bulge-dominated disk (61) galaxies in the redshift range 0.2<z<1.2, selected on the basis of visual morphology from the northern field of the Great Observatories Origins Deep Survey (GOODS-N). We discuss sample selection, photometric properties, and spectral reduction. We derive scale lengths, surface brightnesses, and photometric inhomogeneities from the ACS data and redshifts, stellar velocity dispersions, and [OII] and H{delta} equivalent widths from the Keck spectroscopy. Using the published 2Ms Chandra Deep Field-North X-ray catalog (Cat. <J/AJ/126/632>), we identify active galactic nuclei (AGNs) to clarify the origin of emission lines seen in the Keck spectra.
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