The Euclid space telescope will observe ~10 super(5) strong galaxy-galaxy gravitational lens events in its wide field imaging survey over around half the sky, but identifying the gravitational lenses ...from their observed morphologies requires solving the difficult problem of reliably separating the lensed sources from contaminant populations, such as tidal tails, as well as presenting challenges for spectroscopic follow-up redshift campaigns. Here I present alternative selection techniques for strong gravitational lenses in both Euclid and the Square Kilometre Array, exploiting the strong magnification bias present in the steep end of the Ha luminosity function and the H I mass function. Around 10 super(3) strong lensing events are detectable with this method in the Euclid wide survey. While only ~1% of the total haul of Euclid lenses, this sample has ~100% reliability, known source redshifts, high signal-to-noise, and a magnification-based selection independent of assumptions of lens morphology. With the proposed Square Kilometre Array dark energy survey, the numbers of reliable strong gravitational lenses with source redshifts can reach 10 super(5).
Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we conducted a program to measure redshifts for 13 bright galaxies detected in the
Herschel
Astrophysical Large Area Survey with
S
500
μ
m
...≥ 80 mJy. We report reliable spectroscopic redshifts for 12 individual sources, which are derived from scans of the 3 and 2 mm bands, covering up to 31 GHz in each band, and are based on the detection of at least two emission lines. The spectroscopic redshifts are in the range 2.08 <
z
< 4.05 with a median value of
z
= 2.9 ± 0.6. The sources are unresolved or barely resolved on scales of 10 kpc. In one field, two galaxies with different redshifts were detected. In two cases the sources are found to be binary galaxies with projected distances of ∼140 kpc. The linewidths of the sources are large, with a mean value for the full width at half maximum of 700 ± 300 km s
−1
and a median of 800 km s
−1
. We analyze the nature of the sources with currently available ancillary data to determine if they are lensed or hyper-luminous (
L
FIR
> 10
13
L
⊙
) galaxies. We also present a reanalysis of the spectral energy distributions including the continuum flux densities measured at 3 and 2 mm to derive the overall properties of the sources. Future prospects based on these efficient measurements of redshifts of high-
z
galaxies using NOEMA are outlined, including a comprehensive survey of all the brightest
Herschel
galaxies.
Large-scale imaging surveys will increase the number of galaxy-scale strong lensing candidates by maybe three orders of magnitudes beyond the number known today. Finding these rare objects will ...require picking them out of at least tens of millions of images, and deriving scientific results from them will require quantifying the efficiency and bias of any search method. To achieve these objectives automated methods must be developed. Because gravitational lenses are rare objects, reducing false positives will be particularly important. We present a description and results of an open gravitational lens finding challenge. Participants were asked to classify 100 000 candidate objects as to whether they were gravitational lenses or not with the goal of developing better automated methods for finding lenses in large data sets. A variety of methods were used including visual inspection, arc and ring finders, support vector machines (SVM) and convolutional neural networks (CNN). We find that many of the methods will be easily fast enough to analyse the anticipated data flow. In test data, several methods are able to identify upwards of half the lenses after applying some thresholds on the lens characteristics such as lensed image brightness, size or contrast with the lens galaxy without making a single false-positive identification. This is significantly better than direct inspection by humans was able to do. Having multi-band, ground based data is found to be better for this purpose than single-band space based data with lower noise and higher resolution, suggesting that multi-colour data is crucial. Multi-band space based data will be superior to ground based data. The most difficult challenge for a lens finder is differentiating between rare, irregular and ring-like face-on galaxies and true gravitational lenses. The degree to which the efficiency and biases of lens finders can be quantified largely depends on the realism of the simulated data on which the finders are trained.
Abstract
We model the z ≥ 6.6 Ly α luminosity function to estimate the number of lensed high-z Ly α emitters that may be detected by the Euclid Deep Survey. To span the whole range of possible ...predictions, we exploit two Ly α luminosity function models and two strong gravitational lensing models from the literature. We show that the planned Euclid Deep Survey observing 40 deg2 over the 920–1850 nm wavelength range down to a flux limit of F
lim = 5 × 10−17 erg s−1 cm−2 will enable us to find between ∼0.85 and ∼1.82 deg−2 lensed Ly α emitters at z ≥ 6.6 depending on the adopted Ly α luminosity function and strong gravitational lensing model. The obvious O ii, O iii and H β contaminants of the Ly α lensed population will be identified with the help of Euclid's spectral resolving power, while the Square Kilometre Array (SKA) will enable the identification of the interloper population of H α emitters. By combining Euclid and the SKA, we will thus be able to identify, for the first time, a sample of ∼34 to ∼73 lensed Ly α emitters at z ≥ 6.6.
Exploiting the sensitivity of the IRAM NOrthern Extended Millimeter Array (NOEMA) and its ability to process large instantaneous bandwidths, we have studied the morphology and other properties of the ...molecular gas and dust in the star forming galaxy, H-ATLAS J131611.5+281219 (HerBS-89a), at
z
= 2.95. High angular resolution (0
.
″3) images reveal a partial 1
.
″0 diameter Einstein ring in the dust continuum emission and the molecular emission lines of
12
CO(9−8) and H
2
O(2
02
− 1
11
). Together with lower angular resolution (0
.
″6) images, we report the detection of a series of molecular lines including the three fundamental transitions of the molecular ion OH
+
, namely (1
1
− 0
1
), (1
2
− 0
1
), and (1
0
− 0
1
), seen in absorption; the molecular ion CH
+
(1 − 0) seen in absorption, and tentatively in emission; two transitions of amidogen (NH
2
), namely (2
02
− 1
11
) and (2
20
− 2
11
) seen in emission; and HCN(11 − 10) and/or NH(1
2
− 0
1
) seen in absorption. The NOEMA data are complemented with Very Large Array data tracing the
12
CO(1 − 0) emission line, which provides a measurement of the total mass of molecular gas and an anchor for a CO excitation analysis. In addition, we present
Hubble
Space Telescope imaging that reveals the foreground lensing galaxy in the near-infrared (1.15
μ
m). Together with photometric data from the Gran Telescopio Canarias, we derive a photometric redshift of
z
phot
= 0.9
−0.5
+0.3
for the foreground lensing galaxy. Modeling the lensing of HerBS-89a, we reconstruct the dust continuum (magnified by a factor
μ
≃ 5.0) and molecular emission lines (magnified by
μ
∼ 4 − 5) in the source plane, which probe scales of ∼0
.
″1 (or 800 pc). The
12
CO(9 − 8) and H
2
O(2
02
− 1
11
) emission lines have comparable spatial and kinematic distributions; the source-plane reconstructions do not clearly distinguish between a one-component and a two-component scenario, but the latter, which reveals two compact rotating components with sizes of ≈1 kpc that are likely merging, more naturally accounts for the broad line widths observed in HerBS-89a. In the core of HerBS-89a, very dense gas with
n
H
2
∼ 10
7 − 9
cm
−3
is revealed by the NH
2
emission lines and the possible HCN(11 − 10) absorption line. HerBS-89a is a powerful star forming galaxy with a molecular gas mass of
M
mol
= (2.1 ± 0.4) × 10
11
M
⊙
, an infrared luminosity of
L
IR
= (4.6 ± 0.4) × 10
12
L
⊙
, and a dust mass of
M
dust
= (2.6 ± 0.2) × 10
9
M
⊙
, yielding a dust-to-gas ratio
δ
GDR
≈ 80. We derive a star formation rate SFR = 614 ± 59
M
⊙
yr
−1
and a depletion timescale
τ
depl
= (3.4 ± 1.0) × 10
8
years. The OH
+
and CH
+
absorption lines, which trace low (∼100 cm
−3
) density molecular gas, all have their main velocity component red-shifted by Δ
V
∼ 100 km s
−1
relative to the global CO reservoir. We argue that these absorption lines trace a rare example of gas inflow toward the center of a galaxy, indicating that HerBS-89a is accreting gas from its surroundings.
ABSTRACT
We present spectroscopic measurements for 71 galaxies associated with 62 of the brightest high-redshift submillimetre sources from the Southern fields of the Herschel Astrophysical Terahertz ...Large Area Survey (H-ATLAS), while targeting 85 sources which resolved into 142. We have obtained robust redshift measurements for all sources using the 12-m Array and an efficient tuning of ALMA to optimize its use as a redshift hunter, with 73 per cent of the sources having a robust redshift identification. Nine of these redshift identifications also rely on observations from the Atacama Compact Array. The spectroscopic redshifts span a range 1.41 < z < 4.53 with a mean value of 2.75, and the CO emission line full-width at half-maxima range between $\rm 110\, km\, s^{-1} \lt FWHM \lt 1290\, km\, s^{-1}$ with a mean value of ∼500 km s−1, in line with other high-z samples. The derived CO(1-0) luminosity is significantly elevated relative to line-width to CO(1-0) luminosity scaling relation, which is suggestive of lensing magnification across our sources. In fact, the distribution of magnification factors inferred from the CO equivalent widths is consistent with expectations from galaxy–galaxy lensing models, though there is a hint of an excess at large magnifications that may be attributable to the additional lensing optical depth from galaxy groups or clusters.
Exploiting the Herschel Astrophysical Terahertz Large Area Survey Science Demonstration Phase survey data, we have determined the luminosity functions (LFs) at rest-frame wavelengths of 100 and 250 ...Delta *mm and at several redshifts z 1, for bright submillimeter galaxies with star formation rates (SFRs) 100 M yr--1. We find that the evolution of the comoving LF is strong up to z 2.5, and slows down at higher redshifts. From the LFs and the information on halo masses inferred from clustering analysis, we derived an average relation between SFR and halo mass (and its scatter). We also infer that the timescale of the main episode of dust-enshrouded star formation in massive halos (M H 3 X 1012 M ) amounts to ~7 X 108 yr. Given the SFRs, which are in the range of 102-103 M yr--1, this timescale implies final stellar masses of the order of 1011-1012 M . The corresponding stellar mass function matches the observed mass function of passively evolving galaxies at z 1. The comparison of the statistics for submillimeter and UV-selected galaxies suggests that the dust-free, UV bright phase is 102 times shorter than the submillimeter bright phase, implying that the dust must form soon after the onset of star formation. Using a single reference spectral energy distribution (SED; the one of the z 2.3 galaxy SMM J2135-0102), our simple physical model is able to reproduce not only the LFs at different redshifts >1 but also the counts at wavelengths ranging from 250 Delta *mm to 1 mm. Owing to the steepness of the counts and their relatively broad frequency range, this result suggests that the dispersion of submillimeter SEDs of z > 1 galaxies around the reference one is rather small.
ABSTRACT
Using the Eight MIxer Receiver (EMIR) instrument on the Institut de RadioAstronomie Millimétrique (IRAM) 30-m telescope, we conducted a spectroscopic redshift search of seven zphot ∼ 4 ...submillimetre bright galaxies selected from the Herschel Bright Sources sample with fluxes at 500 μm greater than 80 mJy. For four sources, we obtained spectroscopic redshifts between 3.4 < z < 4.1 through the detection of multiple CO-spectral lines with J ≥ 3. Later, we detected low-J transitions for two of these sources with the Green Bank Telescope including the CO(1–0) transition. For the remaining three sources, more data are needed to determine the spectroscopic redshift unambiguously. The measured CO luminosities and line widths suggest that all these sources are gravitationally lensed. These observations demonstrate that the 2 mm window is indispensable to confirm robust spectroscopic redshifts for z < 4 sources. Finally, we present an efficient graphical method to correctly identify spectroscopic redshifts.
We present a study of the molecular gas properties in a sample of 98 H i – flux selected spiral galaxies within ∼25 Mpc, using the CO J = 3 − 2 line observed with the James Clerk Maxwell Telescope. ...We use the technique of survival analysis to incorporate galaxies with CO upper limits into our results. Comparing the group and Virgo samples, we find a larger mean H2 mass in the Virgo galaxies, despite their lower mean H i mass. This leads to a significantly higher H2 to H i ratio for Virgo galaxies. Combining our data with complementary Hα star formation rate measurements, Virgo galaxies have longer molecular gas depletion times compared to group galaxies, due to their higher H2 masses and lower star formation rates. We suggest that the longer depletion times may be a result of heating processes in the cluster environment or differences in the turbulent pressure. From the full sample, we find that the molecular gas depletion time has a positive correlation with the stellar mass, indicative of differences in the star formation process between low- and high-mass galaxies, and a negative correlation between the molecular gas depletion time and the specific star formation rate.
ABSTRACT Exploiting the sensitivity and spatial resolution of the Atacama Large Millimeter/submillimeter Array, we have studied the morphology and the physical scale of the interstellar medium-both ...gas and dust-in SGP 38326, an unlensed pair of interacting starbursts at z = 4.425. SGP 38326 is the most luminous star bursting system known at z > 4, with a total IR luminosity of LIR ∼ 2.5 × 1013 L and a star formation rate of ∼ 4500 M yr−1. SGP 38326 also contains a molecular gas reservoir among the most massive yet found in the early universe, and it is the likely progenitor of a massive, red-and-dead elliptical galaxy at z ∼ 3. Probing scales of ∼0 1 or ∼800 pc we find that the smooth distribution of the continuum emission from cool dust grains contrasts with the more irregular morphology of the gas, as traced by the C ii fine structure emission. The gas is also extended over larger physical scales than the dust. The velocity information provided by the resolved C ii emission reveals that the dynamics of the two interacting components of SGP 38326 are each compatible with disk-like, ordered rotation, but also reveals an ISM which is turbulent and unstable. Our observations support a scenario where at least a subset of the most distant extreme starbursts are highly dissipative mergers of gas-rich galaxies.
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