A STEEP FAINT-END SLOPE OF THE UV LUMINOSITY FUNCTION AT z ∼ 2–3: IMPLICATIONS FOR THE GLOBAL STELLAR MASS DENSITY AND STAR FORMATION IN LOW-MASS HALOS

By Naveen A. Reddy, C. Steidel. 2008

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We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (α) of the UV luminosity function (LF) at redshifts 1.9 ⩽ z ⩽ 3.4. Our sample includes >2000 spectroscopic redshifts and ≈31000 LBGs in 31 spatially independent fields over a total area of 3261 arcmin2. These data allow us to select galaxies to 0.07L* and 0.10L* at z ∼ 2 and z ∼ 3, respectively. A maximum-likelihood analysis indicates steep values of α(z = 2) = −1.73 ± 0.07 and α(z = 3) = −1.73 ± 0.13. This result is robust to luminosity-dependent systematics in the Lyα equivalent width and reddening distributions, and is similar to the steep values advocated at z ≳ 4, and implies that ≈93% of the unobscured UV luminosity density at z ∼ 2–3 arises from sub-L* galaxies. With a realistic luminosity-dependent reddening distribution, faint to moderately luminous galaxies account for ≳70% and ≳25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.9 ⩽ z < 3.4. We find a factor of 8–9 increase in the star-formation rate density between z ∼ 6 and z ∼ 2, due to both a brightening of L* and an increasing dust correction proceeding to lower redshifts. Combining the UV LF with stellar mass estimates suggests a relatively steep low-mass slope of the stellar mass function at high redshift. The previously observed discrepancy between the integral of the star-formation history and stellar mass density measurements at z ∼ 2 may be reconciled by invoking a luminosity-dependent reddening correction to the star-formation history combined with an accounting for the stellar mass contributed by UV-faint galaxies. The steep and relatively constant faint-end slope of the UV LF at z ≳ 2 contrasts with the shallower slope inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of low-mass halos capable of supporting star formation at z ≲ 2.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

• A unified multiwavelength model of galaxy formation (2015, unknown): “Observational data are from Arnouts et al. (2005) (crosses),Reddy & Steidel (2009) (filled circles) and Sawicki & Thompson (2006) (open triangles) atz = 3, and Bouwens et al. (2015) (filled circles), Finkelstein et al. (2015) (open triangles) and Shimasaku et al. (2005) (crosses) atz = 6. to the…”
• THE STRUCTURE AND KINEMATICS OF THE CIRCUMGALACTIC MEDIUM FROM FAR-ULTRAVIOLET SPECTRA OF z ≃ 2–3 GALAXIES (2010, methodology): “Reddy & Steidel (2009) have produced the most up-to-date LF, determined from the same data set and using the same selection criteria as the galaxies used in the galaxy-galaxy pair analysis.”
• X-RAY BINARY EVOLUTION ACROSS COSMIC TIME (2012, methodology): “Observational determinations of the SFR density at different redshifts (grey squares) are shown for comparison (Schiminovich et al. 2005; Bouwenset al. 2007; Reddy & Steidel 2009).”
• Galaxy Zoo Green Peas: discovery of a class of compact extremely star-forming galaxies (2009, background): “%) of the present day stellar mass (Reddy & Steidel 2009).”
• GALAXY STELLAR MASS FUNCTIONS FROM ZFOURGE/CANDELS: AN EXCESS OF LOW-MASS GALAXIES SINCE z = 2 AND THE RAPID BUILDUP OF QUIESCENT GALAXIES (2013, methodology): “We compare our z > 2 measurements to estimates based on the Reddy & Steidel (2009) measurements in Figure 12.”
• The contribution of high-redshift galaxies to cosmic reionization: New results from deep WFC3 imaging of the Hubble Ultra Deep Field (2009, methodology): “At the bright end, this interpretation agrees with the low surface density of z′-band drop-outs found in the HAWK-I imaging of GOODS-South presented in Hickey et 4 Recently, Reddy & Steidel (2009) have re-fit a steeper luminosity function to the z ≈ 3 Lyman-break population, with α = −1.73, φ∗ = 0.0”
• A study of the gas–star formation relation over cosmic time (2010, background): “Since the extinction of high-z SFGs appears to be lower than comparably luminous low-z systems (Daddi et al. 2007; Reddy & Steidel 2009), the applicability of the UV estimator (like that of Hα) appears well justified for most z ≥ 1 SFGs.”
• THE STAR FORMATION HISTORY OF MASS-SELECTED GALAXIES IN THE COSMOS FIELD (2010, background): “Recent UV-based measurements (Reddy & Steidel 2009; Bouwens et al. 2010) suggest a peak of the CSFH at around z = 2 − 2.5 and assume that the dust obscuration for the bulk of SF galaxies does not dramatically change out to z ∼ 4 (as shown by e.g. Bouwens et al. 2009; Finkelstein et al. 2009; McLure…”
• The evolution of massive black holes and their spins in their galactic hosts (2012, background): “There are various possible explanations for this discrepancy, namely uncertainties in the effect of dust on the stellar-mass and SFR estimates at high-redshifts (Driver et al. 2007), or incompleteness in the measured stellar-mass density (Reddy & Steidel 2009).”
• REGULARITY UNDERLYING COMPLEXITY: A REDSHIFT-INDEPENDENT DESCRIPTION OF THE CONTINUOUS VARIATION OF GALAXY-SCALE MOLECULAR GAS PROPERTIES IN THE MASS-STAR FORMATION RATE PLANE (2013, unknown): “…Bouché et al. 2010, Peng et al. 2010, Leitner 2012, Behroozi et al. 2013) and that the strong decline of the cosmic SFR density since z∼ 2 (e.g., Reddy & Steidel 2009, Rodighiero et al. 2010, Karim et al. 2011, Magnelli et al. 2011, Cucciati et al. 2012; and references therein) reflects the…”
• AN INTENSELY STAR-FORMING GALAXY AT z ∼ 7 WITH LOW DUST AND METAL CONTENT REVEALED BY DEEP ALMA AND HST OBSERVATIONS (2013, background): “…small galaxies at high redshift also indicates significant merging occurred at early times, given the faint-end slope of the UV luminosity function changes from a steep α ≃ −1.9 at z = 7 − 8 (Schenker et al. 2012; McLure et al. 2012) to α ≃ −1.7 at z = 2− 3 (e.g. Reddy & Steidel 2009).”
• HERSCHEL-ATLAS GALAXY COUNTS AND HIGH-REDSHIFT LUMINOSITY FUNCTIONS: THE FORMATION OF MASSIVE EARLY-TYPE GALAXIES (2011, result): “A comparison of our LFs with the UV ones at z ≈ 2−3 (Sawicki & Thompson 2005; Reddy & Steidel 2009) for galaxies with comparable SFRs shows that the UV space densities are a factor & 100 lower, implying that the UV bright, dust-free phase is much shorter than the farIR bright phase.”
• A Universal Stellar Initial Mass Function? A critical look at variations in extreme environments (2010, background): “Using a large UV survey of Lyman Break Galaxies in the redshift range z = 2− 3, Reddy & Steidel (2009) find a much steeper luminosity function than earlier measurements, meaning that low luminosity galaxies make up a larger fraction of the mass density of the Universe at high redshift than…”