THE CHARACTERISTIC STAR FORMATION HISTORIES OF GALAXIES AT REDSHIFTS z ∼ 2–7

By Naveen A. Reddy, M. Pettini, C. Steidel, A. Shapley, D. Erb, D. Law. 2012

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A large sample of spectroscopically confirmed star-forming galaxies at redshifts 1.4 ⩽ zspec ⩽ 3.7, with complementary imaging in the near- and mid-IR from the ground and from the Hubble Space Telescope and Spitzer Space Telescope, is used to infer the average star formation histories (SFHs) of typical galaxies from z ∼ 2 to 7. For a subset of 302 galaxies at 1.5 ⩽ zspec < 2.6, we perform a detailed comparison of star formation rates (SFRs) determined from spectral energy distribution (SED) modeling (SFRs[SED]) and those calculated from deep Keck UV and Spitzer/MIPS 24 μm imaging (SFRs[IR+UV]). Exponentially declining SFHs yield SFRs[SED] that are 5–10 times lower on average than SFRs[IR+UV], indicating that declining SFHs may not be accurate for typical galaxies at z ≳ 2. The SFRs of z ∼ 2–3 galaxies are directly proportional to their stellar masses (M*), with unity slope—a result that is confirmed with Spitzer/IRAC stacks of 1179 UV-faint (25.5$?>) galaxies—for M* ≳ 5 × 108 M☉ and SFRs ≳ 2 M☉ yr−1. We interpret this result in the context of several systematic biases that can affect determinations of the SFR–M* relation. The average specific SFRs at z ∼ 2–3 are remarkably similar within a factor of two to those measured at z ≳ 4, implying that the average SFH is one where SFRs increase with time. A consequence of these rising SFHs is that (1) a substantial fraction of UV-bright z ∼ 2–3 galaxies had faint sub-L* progenitors at z ≳ 4; and (2) gas masses must increase with time from z = 2 to 7, over which time the net cold gas accretion rate—as inferred from the specific SFR and the Kennicutt–Schmidt relation—is ∼2–3 times larger than the SFR. However, if we evolve to higher redshift the SFHs and masses of the halos that are expected to host L* galaxies at z ∼ 2, then we find that ≲ 10% of the baryons accreted onto typical halos at z ≳ 4 actually contribute to star formation at those epochs. These results highlight the relative inefficiency of star formation even at early cosmic times when galaxies were first assembling.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

• A HIGHLY CONSISTENT FRAMEWORK FOR THE EVOLUTION OF THE STAR-FORMING “MAIN SEQUENCE” FROM z ∼ 0–6 (2014, background): “…(MS) generally takes the form logψ = α logM∗ + β, (1) with α and β free parameters of the fit. α is usually measured to be between 0 and 1 (Chen et al. 2009; Reddy et al. 2012a (R12a)), with values of ∼ 0.6 – 1 preferred (Rodighiero et al. 2011), and both α (MS slope, i.e. power-law index) and…”
• A LINK BETWEEN STAR FORMATION QUENCHING AND INNER STELLAR MASS DENSITY IN SLOAN DIGITAL SKY SURVEY CENTRAL GALAXIES (2013, background): “This effect has been called “outshining” in some contexts (Reddy et al. 2012; Wuyts et al. 2012), whereby light from recently formed stars biases measurements of radii, stellar population ages, or other parameters.”
• KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY (2012, background): “For each realisation of the UV LF, we draw a UV slope, β, by adopting the redshift-dependent β − MUV scaling relationships (Bouwens et al. 2012b).”
• THE SPECTRAL ENERGY DISTRIBUTIONS OF z ∼ 8 GALAXIES FROM THE IRAC ULTRA DEEP FIELDS: EMISSION LINES, STELLAR MASSES, AND SPECIFIC STAR FORMATION RATES AT 650 MYR (2012, unknown): “{TheWHα based sSFR= 11 +11 −5 Gyr −1 are∼ 5× higher than those at z = 2 (Reddy et al. 2012), consistent with an increase sSFR ∝ (1 + z)1.5 +0.7 −0.5 between 2 < z < 8.”
• The mass evolution of the first galaxies: stellar mass functions and star formation rates at 4 < z < 7 in the CANDELS GOODS-South field (2014, result): “If we include the additional observations of Daddi et al. (2007) and Reddy et al. (2012), we find a best-fit of sSFR ∝ (1 + z)0.9 ± 0.2, consistent with that found by González et al. (2014).”
• Inferring the star formation histories of massive quiescent galaxies with bagpipes: evidence for multiple quenching mechanisms (2017, background): “The main advantage of this rigid parameterisation is the speed of fitting, however Maraston et al. (2010) and Reddy et al. (2012) have shown by that it becomes less effective at higher redshifts, and Wuyts et al. (2011) and Pforr et al. (2012) have shown that the biases on the estimated SFH…”
• THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ⩽ z ⩽ 6.5 IN CANDELS (2014, methodology): “Previous works have shown that broadband SED fitting offers no statistical preference between constant, rising, or declining star-formation histories, even with broadband coverage spanning to the IR (Reddy et al. 2012).”
• THE AVERAGE STAR FORMATION HISTORIES OF GALAXIES IN DARK MATTER HALOS FROM z = 0–8 (2012, unknown): “4GHz <0.025 deg2 I Salmi et al. (2012) 0.9− 1.3 U-IR <0.025 deg2 Karim et al. (2011) 0.2− 3 1.4 GHz 2 deg2 Kajisawa et al. (2010) 0.5− 3.5 UV/IR 0.029 deg2 I Reddy et al. (2012) 1.4− 3.7 UV/IR 0.44 deg2 I Lee et al. (2011) 3.”
• The Herschel* PEP/HerMES luminosity function - I. Probing the evolution of PACS selected Galaxies to z ≃ 4 (2013, result): “…declining SFR might not be the best to reproduce the SFR history of z>1.5 star-forming galaxies (i.e. exponentially increasing or increasing SFR would be better choices, as widely discussed by Maraston et al. 2010 and Reddy et al. 2012), in our specific case it does not affect the results.”
• Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7 (2014, methodology): “The UV-continuum slope (parameterized asβ wherefλ ∝ λβ) provides a unique constraint on the dust extinction in high-redshift UV-selected galaxies (e.g., Reddy et al. 2012a) and is additionally affected by the metallicity and age of the stellar population.”
• THE MOSDEF SURVEY: MASS, METALLICITY, AND STAR-FORMATION RATE AT z ∼ 2.3 (2014, background): “There is some evidence in the literature of extreme accretion rates at z & 2, as suggested by gas mass fractions and sSFR (Tacconi et al. 2010, 2013; Reddy et al. 2012).”
• VALIDATION OF THE EQUILIBRIUM MODEL FOR GALAXY EVOLUTION TO z ∼ 3 THROUGH MOLECULAR GAS AND DUST OBSERVATIONS OF LENSED STAR-FORMING GALAXIES (2013, methodology): “Such studies indeed suggest a rise in temperature and intensity of the radiation field on the main sequence in the mass/redshift regime that we have now probed directly with the lensed galaxies (Reddy et al. 2012; Magdis et al. 2012a; Magnelli et al. 2013).”
• THE SFR–M* RELATION AND EMPIRICAL STAR FORMATION HISTORIES FROM ZFOURGE AT 0.5 < z < 4 (2015, result): “Several recent studies have also found evidence in support of rising SFHs in individual galaxies at early times (e.g. Papovich et al. 2011; Reddy et al. 2012; Lee et al. 2011; Abramson et al. 2015).”
• The Star Formation Main Sequence in the Hubble Space Telescope Frontier Fields (2017, result): “…z ∼ 2 (e.g. Noeske et al. 2007; Santini et al. 2009; Karim et al. 2011) and flattened at higher redshift (e.g. Stark et al. 2009; González et al. 2010; Reddy et al. 2012; González et al. 2010; Labbé et al. 2010; McLure et al. 2011), in sharp contrast with theoretical predictions (see e.g.…”
• Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio (2016, methodology): “Additionally, although age estimates from SED fitting are not very robust in an absolute sense, 15% of large-offset galaxies have SEDs that are best fit by a constant star forma- tion history with an age of 50 Myr, compared to only 3% of small-offset galaxies; as discussed in §2.5, this age is a min”
• THE MOSDEF SURVEY: MEASUREMENTS OF BALMER DECREMENTS AND THE DUST ATTENUATION CURVE AT REDSHIFTS z ∼ 1.4–2.6 (2015, methodology): “The stacking of mid- and far-IR data from the Spitzer Space Telescope and the Herschel Space Observatory has proved beneficial for our understanding of the average dust properties of typical L∗ star-forming galaxies at z ∼ 2 (Reddy et al. 2006; Daddi et al. 2007; Reddy et al. 2012a).”
• THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3 (2015, background): “As described in Section 3.5, the z ∼ 2.3 galaxies span a similar range in M∗ as local SDSS galaxies, but have significantly higher SFR and sSFR at a given stellar mass, consistent with the evolution of the SFR-M∗ relation with redshift (Reddy et al. 2012; Whitaker et al. 2014; Shivaei et al. 2015).”
• Star formation sustained by gas accretion (2014, background): “Observations of this imbalance were suggested by Reddy et al. (2012) who found at z > 2 an accretion rate from the KS relation that is 2 to 3 times larger than the SFR during galaxy build-up.”