An official website of the United States government
Abstract In this work, we publish stellar velocity dispersions, sizes, and dynamical masses for eight ultramassive galaxies (UMGs; > 11),z≳ 3) from the Massive Ancient Galaxies Atz> 3 NEar-infrared (MAGAZ3NE) Survey, more than doubling the number of such galaxies with velocity dispersion measurements at this epoch. Using the deep Keck/MOSFIRE and Keck/NIRES spectroscopy of these objects in theHandKbandpasses, we obtain large velocity dispersions of ∼400 km s−1for most of the objects, which are some of the highest stellar velocity dispersions measured and ∼40% larger than those measured for galaxies of similar mass atz∼ 1.7. The sizes of these objects are also smaller by a factor of 1.5–3 compared to this samez∼ 1.7 sample. We combine these large velocity dispersions and small sizes to obtain dynamical masses. The dynamical masses are similar to the stellar masses of these galaxies, consistent with a Chabrier initial mass function (IMF). Considered alongside previous studies of massive quiescent galaxies across 0.2 <z< 4.0, there is evidence for an evolution in the relation between the dynamical mass–stellar mass ratio and velocity dispersion as a function of redshift. This implies an IMF with fewer low-mass stars (e.g., Chabrier IMF) for massive quiescent galaxies at higher redshifts in conflict with the bottom-heavy IMF (e.g., Salpeter IMF) found in their likelyz∼ 0 descendants, though a number of alternative explanations such as a different dynamical structure or significant rotation are not ruled out. Similar to data at lower redshifts, we see evidence for an increase of IMF normalization with velocity dispersion, though thez≳ 3 trend is steeper than that forz∼ 0.2 early-type galaxies and offset to lower dynamical-to-stellar mass ratios.
more »
« less
The Heavy Metal Survey: Star Formation Constraints and Dynamical Masses of 21 Massive Quiescent Galaxies at z = 1.3–2.3
Abstract In this paper, we present the Heavy Metal Survey, which obtained ultradeep medium-resolution spectra of 21 massive quiescent galaxies at 1.3 <z< 2.3 with Keck/LRIS and MOSFIRE. With integration times of up to 16 hr per band per galaxy, we observe numerous Balmer and metal absorption lines in atmospheric windows. We successfully derive spectroscopic redshifts for all 21 galaxies, and for 19 we also measure stellar velocity dispersions (σv), ages, and elemental abundances, as detailed in an accompanying paper. Except for one emission-line active galactic nucleus, all galaxies are confirmed as quiescent through their faint or absent Hαemission and evolved stellar spectra. For most galaxies exhibiting faint Hα, elevated [Nii]/Hαsuggests a non-star-forming origin. We calculate dynamical masses (Mdyn) by combiningσvwith structural parameters obtained from the Hubble Space Telescope COSMOS(-DASH) survey and compare them with stellar masses (M*) derived using spectrophotometric modeling, considering various assumptions. For a fixed initial mass function (IMF), we observe a strong correlation betweenMdyn/M*andσv. This correlation may suggest that a varying IMF, with high-σvgalaxies being more bottom heavy, was already in place atz∼ 2. When implementing theσv-dependent IMF found in the cores of nearby early-type galaxiesandcorrecting for biases in our stellar mass and size measurements, we find a low scatter inMdyn/M*of 0.14 dex. However, these assumptions result in unphysical stellar masses, which exceed the dynamical masses by 34%. This tension suggests that distant quiescent galaxies do not simply grow inside-out into today’s massive early-type galaxies and the evolution is more complicated.
more »
« less
- Award ID(s):
- 1908748
- PAR ID:
- 10502173
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 966
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 36
- Size(s):
- Article No. 36
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Deep Very Large Telescope/MUSE optical integral field spectroscopy has recently revealed an abundant population of ultra-faint galaxies (MUV≈ −15; 0.01L⋆) atz= 2.9−6.7 due to their strong Lyαemission with no detectable continuum. The implied Lyαequivalent widths can be in excess of 100–200 Å, challenging existing models of normal star formation and indicating extremely young ages, small stellar masses, and a very low amount of metal enrichment. We use JWST/NIRSpec’s microshutter array to follow up 45 of these galaxies (11 hr in G235M/F170LP and 7 hr in G395M/F290LP), as well as 45 lower-equivalent width Lyαemitters. Our spectroscopy covers the range 1.7−5.1 micron in order to target strong optical emission lines: Hα, [Oiii], Hβ, and [N II]. Individual measurements as well as stacks reveal line ratios consistent with a metal-poor nature (2%−40%Z⊙, depending on the calibration). The galaxies with the highest equivalent widths of Lyα, in excess of 90 Å, have lower [N II]/Hα(1.9σ) and [Oiii]/Hβ(2.2σ) ratios than those with lower equivalent widths, implying lower gas-phase metallicities at a combined significance of 2.4σ. This implies a selection based on Lyαequivalent width is an efficient technique for identifying younger, less chemically enriched systems.more » « less
-
Abstract We present the elemental abundances and ages of 19 massive quiescent galaxies atz∼ 1.4 andz∼ 2.1 from the Keck Heavy Metal Survey. The ultradeep LRIS and MOSFIRE spectra were modeled using a full-spectrum stellar population fitting code with variable abundance patterns. The galaxies have iron abundances between [Fe/H] = −0.5 and −0.1 dex, with typical values of −0.2 [−0.3] atz∼ 1.4 [z∼ 2.1]. We also find a tentative –[Fe/H] relation atz∼ 1.4. The magnesium-to-iron ratios span [Mg/Fe] = 0.1–0.6 dex, with typical values of 0.3 [0.5] dex atz∼ 1.4 [z∼ 2.1]. The ages imply formation redshifts ofzform= 2–8. Compared to quiescent galaxies at lower redshifts, we find that [Fe/H] was ∼0.2 dex lower atz= 1.4–2.1. We find no evolution in [Mg/Fe] out toz∼ 1.4, though thez∼ 2.1 galaxies are 0.2 dex enhanced compared toz= 0–0.7. A comparison of these results to a chemical evolution model indicates that galaxies at higher redshift form at progressively earlier epochs and over shorter star formation timescales, with thez∼ 2.1 galaxies forming the bulk of their stars over 150 Myr atzform∼ 4. This evolution cannot be solely attributed to an increased number of quiescent galaxies at later times; several Heavy Metal galaxies have extreme chemical properties not found in massive galaxies atz∼ 0.0–0.7. Thus, the chemical properties of individual galaxies must evolve over time. Minor mergers also cannot fully account for this evolution as they cannot increase [Fe/H], particularly in galaxy centers. Consequently, the buildup of massive quiescent galaxies sincez∼ 2.1 may require further mechanisms, such as major mergers and/or central star formation.more » « less
-
Abstract We present kinematics of six local extremely metal-poor galaxies (EMPGs) with low metallicities (0.016–0.098Z⊙) and low stellar masses (104.7–107.6M⊙). Taking deep medium/high-resolution (R∼ 7500) integral-field spectra with 8.2 m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hαemission. Carefully masking out substructures originating by inflow and/or outflow, we fit three-dimensional disk models to the observed Hαflux, velocity, and velocity dispersion maps. All the EMPGs show rotational velocities (vrot) of 5–23 km s−1smaller than the velocity dispersions (σ0) of 17–31 km s−1, indicating dispersion-dominated (vrot/σ0= 0.29–0.80 < 1) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions offgas≃ 0.9–1.0. Comparing our results with other Hαkinematics studies, we find thatvrot/σ0decreases andfgasincreases with decreasing metallicity, decreasing stellar mass, and increasing specific star formation rate. We also find that simulated high-z(z∼ 7) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope observations atz∼ 7.more » « less
-
Abstract We use the H41αrecombination line to create templates of the millimeter free–free emission in the ALMA-IMF continuum maps, which allows us to separate it from dust emission. This method complements spectral-index information and extrapolation from centimeter-wavelength maps. We use the derived maps to estimate the properties of up to 34 Hiiregions across the ALMA-IMF protoclusters. The hydrogen ionizing photon rateQ0and spectral types follow the evolutionary trend proposed by Motte et al. The youngest protoclusters lack detectable ionized gas, followed by protoclusters with increasing numbers of OB stars. The totalQ0increases from ∼1045s−1to >1049s−1. We used the adjacent He41αline to measure the relative number abundances of helium, finding values consistent with the Galactic interstellar medium, although a few outliers are discussed. A search for sites of maser amplification of the H41αline returned negative results. We looked for possible correlations between the electron densities, emission measures, andQ0with Hiiregion sizeD. The latter is the best correlated, withQ0∝D2.49 ± 0.18. This favors interpretations in which smaller ultracompact Hiiregions are not necessarily the less dynamically evolved versions of larger ones but rather are ionized by less massive stars. Moderate correlations were found between the dynamical width ΔVdynwithDandQ0. ΔVdynincreases from about 1 to 2 times the ionized-gas sound speed. Finally, an outlier Hiiregion south of W43-MM2 is discussed. We suggest that this source could harbor an embedded stellar or disk wind.more » « less
