Prof. Dimitra Rigopoulou

Abstract:

We present millimetre dust emission measurements of two Lyman-break galaxies at z ∼ 3 and construct for the first time fully sampled infrared spectral energy distributions (SEDs), from mid-IR to the Rayleigh-Jeans tail, of individually detected, unlensed, UV-selected, main sequence (MS) galaxies at z = 3. The SED modelling of the two sources confirms previous findings, based on stacked ensembles, of an increasing mean radiation field (U) with redshift, consistent with a rapidly decreasing gas metallicity in z > 2 galaxies. Complementing our study with CO[J = 3 → 2] emission line observations, we have measured the molecular gas mass reservoir (M H 2 ) of the systems using three independent approaches: 1) CO line observations; 2) the dust to gas mass ratio vs. metallicity relation; and 3) a single band, dust emission flux on the Rayleigh-Jeans side of the SED. All techniques return consistent M H 2 estimates within a factor of two or less, yielding gas depletion time-scales (τ dep ≈ 0.35 Gyr) and gas-to-stellar mass ratios (M H 2 /M ∗ ≈ 0.5-1) for our z ∼ 3 massive MS galaxies. The overall properties of our galaxies are consistent with trends and relations established at lower redshifts, extending the apparent uniformity of star-forming galaxies over the last 11.5 billion years.

Abstract:

We present the results from Atacama Large Millimeter/submillimeter Array imaging in the [N ii] 205μm fine-structure line (hereafter [N ii] ) and the underlying continuum of BRI 1202-0725, an interacting galaxy system at z = 4.7, consisting of a quasi-stellar object (QSO), a submillimeter galaxy (SMG), and two Ly emitters, all within ∼25 kpc of the QSO. We detect the QSO and SMG in both [N ii] and continuum. At the ∼1″ (or 6.6 kpc) resolution, both the QSO and SMG are resolved in [N ii] , with the de-convolved major axes of ∼9 and ∼14 kpc, respectively. In contrast, their continuum emissions are much more compact and unresolved even at an enhanced resolution of ∼0.″7. The ratio of the [N ii] flux to the existing CO(7-6) flux is used to constrain the dust temperature (T dust ) for a more accurate determination of the FIR luminosity LFIR . Our best estimated T dust equals 43 (±2) K for both galaxies (assuming an emissivity index β = 1.8). The resulting LCO(7-6) /L FIR ratios are statistically consistent with that of local luminous infrared galaxies, confirming that LCO(7-6) traces the star formation (SF) rate (SFR) in these galaxies. We estimate that the ongoing SF of the QSO (SMG) has an SFR of 5.1 (6.9) × 10^3 M⊙ yr^-1 (±30%) assuming Chabrier initial mass function, takes place within a diameter (at half maximum) of 1.3 (1.5) kpc, and will consume the existing 5 (5) × 10^11 M⊙ of molecular gas in 10 (7) × 10 7 years.