skip to main content


Title: Merger Signatures are Common, but not Universal, in Massive, Recently Quenched Galaxies at z ∼ 0.7
Abstract

We present visual classifications of merger-induced tidal disturbances in 143M*∼ 1011Mpost-starburst galaxies atz∼ 0.7 identified in theSQuIGGLESample. This sample spectroscopically selects galaxies from the Sloan Digital Sky Survey that have stopped their primary epoch of star formation within the past ∼500 Myr. Visual classifications are performed on Hyper Suprime-Cam imaging. We compare to a control sample of mass- and redshift-matched star-forming and quiescent galaxies from the Large Early Galaxy Census and find that post-starburst galaxies are more likely to be classified as disturbed than either category. This corresponds to a factor of3.61.3+2.9times the disturbance rate of older quiescent galaxies and2.1.73+1.9times the disturbance rate of star-forming galaxies. Assuming tidal features persist for ≲500 Myr, this suggests merging is coincident with quenching in a significant fraction of these post-starbursts. Galaxies with tidal disturbances are younger on average than undisturbed post-starburst galaxies in our sample, suggesting tidal features from a major merger may have faded over time. This may be exacerbated by the fact that, on average, the undisturbed subset is fainter, rendering low-surface-brightness tidal features harder to identify. However, the presence of 10 young (≲150 Myr since quenching) undisturbed galaxies suggests that major mergers are not the only fast physical mechanism that shut down the primary epoch of star formation in massive galaxies at intermediate redshift.

 
more » « less
Award ID(s):
1907697
NSF-PAR ID:
10414392
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
949
Issue:
1
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 5
Size(s):
["Article No. 5"]
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    We present a measurement of the intrinsic space density of intermediate-redshift (z∼ 0.5), massive (M*∼ 1011M), compact (Re∼ 100 pc) starburst (ΣSFR∼ 1000Myr−1kpc−1) galaxies with tidal features indicative of them having undergone recent major mergers. A subset of them host kiloparsec-scale, > 1000 km s−1outflows and have little indication of AGN activity, suggesting that extreme star formation can be a primary driver of large-scale feedback. The aim for this paper is to calculate their space density so we can place them in a better cosmological context. We do this by empirically modeling the stellar populations of massive, compact starburst galaxies. We determine the average timescale on which galaxies that have recently undergone an extreme nuclear starburst would be targeted and included in our spectroscopically selected sample. We find that massive, compact starburst galaxies targeted by our criteria would be selectable for14824+27Myr and have an intrinsic space densitynCS(1.10.3+0.5)×106Mpc3. This space density is broadly consistent with ourz∼ 0.5 compact starbursts being the most extremely compact and star-forming low-redshift analogs of the compact star-forming galaxies in the early universe, as well as them being the progenitors to a fraction of intermediate-redshift, post-starburst, and compact quiescent galaxies.

     
    more » « less
  2. Abstract

    We measure the CO-to-H2conversion factor (αCO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofαCOfor CO (2–1) and (1–0), respectively. The mean values forαCO (2–1)andαCO (1–0)are9.35.4+4.6and4.22.0+1.9Mpc2(Kkms1)1, respectively. The CO-intensity-weighted mean is 5.69 forαCO (2–1)and 3.33 forαCO (1–0). We examine howαCOscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength (U¯). Among them,U¯, ΣSFR, and the integrated CO intensity (WCO) have the strongest anticorrelation with spatially resolvedαCO. We provide linear regression results toαCOfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenαCOandWCO, metallicity,U¯, and ΣSFR. We also find thatαCOin each galaxy decreases with the stellar mass surface density (Σ) in high-surface-density regions (Σ≥ 100Mpc−2), following the power-law relationsαCO(21)Σ0.5andαCO(10)Σ0.2. The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inαCOwith increasing Σas a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inαCO. The decrease inαCOat high Σis important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors.

     
    more » « less
  3. Abstract

    We use ALMA observations of CO(2–1) in 13 massive (M*≳ 1011M) poststarburst galaxies atz∼ 0.6 to constrain the molecular gas content in galaxies shortly after they quench their major star-forming episode. The poststarburst galaxies in this study are selected from the Sloan Digital Sky Survey spectroscopic samples (Data Release 14) based on their spectral shapes, as part of the Studying QUenching at Intermediate-z Galaxies: Gas, anguLarmomentum, and Evolution (SQuIGGLE) program. Early results showed that two poststarburst galaxies host large H2reservoirs despite their low inferred star formation rates (SFRs). Here we expand this analysis to a larger statistical sample of 13 galaxies. Six of the primary targets (45%) are detected, withMH2109M. Given their high stellar masses, this mass limit corresponds to an average gas fraction offH2MH2/M*7%or ∼14% using lower stellar masses estimates derived from analytic, exponentially declining star formation histories. The gas fraction correlates with theDn4000 spectral index, suggesting that the cold gas reservoirs decrease with time since burst, as found in local K+A galaxies. Star formation histories derived from flexible stellar population synthesis modeling support this empirical finding: galaxies that quenched ≲150 Myr prior to observation host detectable CO(2–1) emission, while older poststarburst galaxies are undetected. The large H2reservoirs and low SFRs in the sample imply that the quenching of star formation precedes the disappearance of the cold gas reservoirs. However, within the following 100–200 Myr, theSQuIGGLEgalaxies require the additional and efficient heating or removal of cold gas to bring their low SFRs in line with standard H2scaling relations.

     
    more » « less
  4. Abstract

    The warm Neptune GJ 3470b transits a nearby (d= 29 pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak Observatory, we model the classical Rossiter–McLaughlin effect, yielding a sky-projected obliquity ofλ=9812+15and avsini=0.850.33+0.27kms1. Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity ofψ=958+9, revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS, and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term radial velocity (RV) slope ofγ̇=0.0022±0.0011ms1day1over a baseline of 12.9 yr. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b’s mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of ∼1.5–1.7, which could help account for its evaporating atmosphere.

     
    more » « less
  5. Abstract

    We compare 500 pc scale, resolved observations of ionized and molecular gas for thez∼ 0.02 starbursting disk galaxy IRAS08339+6517, using measurements from KCWI and NOEMA. We explore the relationship of the star-formation-driven ionized gas outflows with colocated galaxy properties. We find a roughly linear relationship between the outflow mass flux (Σ̇out) and star formation rate surface density (ΣSFR),Σ̇outΣSFR1.06±0.10, and a strong correlation betweenΣ̇outand the gas depletion time, such thatΣ̇outtdep1.1±0.06. Moreover, we find these outflows are so-calledbreakoutoutflows, according to the relationship between the gas fraction and disk kinematics. Assuming that ionized outflow mass scales with total outflow mass, our observations suggest that the regions of highest ΣSFRin IRAS08 are removing more gas via the outflow than through the conversion of gas into stars. Our results are consistent with a picture in which the outflow limits the ability of a region of a disk to maintain short depletion times. Our results underline the need for resolved observations of outflows in more galaxies.

     
    more » « less