Tom J. Wilson

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Postdoctoral Research Fellow at the University of Exeter, working on cross-matching photometric catalogues in crowded fields as part of the LSST:UK Consortium. Also developing PSF photometry codebase in the astropy-affliated photutils package. Astrostatistician, occasional exoplanet dabbler.

t.j.wilson [at] exeter.ac.uk
CV
ADS Publications
ORCID: 0000-0001-6352-9735
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Schechter Function Parameterisation for Differential Galaxy Counts

Here I provide the data used to construct the galaxy count model described in Wilson (2022, RNAAS, …). The model assumes galaxy luminosities are described by a Schechter function, where the density of galaxies as a function of absolute magnitude in a given bandpass is given by \(\phi(M) = 0.4 \ln(10) \phi^* [10^{-0.4 (M-M^*)}]^{\alpha+1} \exp(-10^{-0.4 (M - M^*)})\), with \(M^*(z) = M^*_0 - Qz\), \(\phi^* = \phi^*_0 10^{0.4 P z}\) describing the redshift dependency of the characteristic absolute magnitude and normalising density of the luminosity function respectively and \(\alpha\) the slope of the faint end of the distribution.

The observed differential galaxy count is then derived by a conversion from \(\phi\) in units of \(\mathrm{Mpc}^{-3}\,\mathrm{mag}^{-1}\) to sky number densities (\(\mathrm{deg}^{-2}\,\mathrm{mag}^{-1}\)) by consideration of differential comoving volume and an integral over all redshifts. Final observed densities of galaxies in a bandpass are the sum of two Schechter functions, \(\phi_\mathrm{tot} = \phi_b + \phi_r\), for “blue” (star-forming) and “red” (quiescent) galaxies, and hence we require a total of 10 parameters to describe the density of galaxies at a particular redshift.

To derive galaxy counts for an arbitrary bandpass, a parameterisation for these 10 parameters – \(M^*_0\), \(\phi^*_0\), \(P\), \(Q\), and \(\alpha\), for both blue and red galaxy distributions – was found as a function of wavelength, with the exception of \(Q\), which – due to the degeneracy between it and \(P\) – was derived as a function of \(P\). The functions used to describe these parameters are \(y(x) = m \times x + c\) for \(Q(P)\), \(\alpha(\log_{10}(\lambda / \mu\mathrm{m}))\), and \(P(\log_{10}(\lambda / \mu\mathrm{m}))\); \(y(x) = a \exp(-m x) + c\) for \(M^*_0(\log_{10}(\lambda / \mu\mathrm{m}))\) and blue galaxy \(\phi^*_0(\log_{10}(\lambda / \mu\mathrm{m}))\); and \(y(x) = a \exp(-0.5 (x - u)^2 \times m) + c\) for red galaxy \(\phi^*_0(\log_{10}(\lambda / \mu\mathrm{m}))\). Note that \(x \equiv \log_{10}(\lambda / \mu\mathrm{m}))\) in four cases, with \(x \equiv P\) solely for the parameterisation of \(Q\). The table below provides the values derived for each parameter fit for both galaxy types, with a machine-readable version of the data available here. A figure showing the first to the parameters, as well as some example differential galaxy counts (see Wilson 2022, RNAAS, … for more details) is also available.

Parameter Galaxy type c m a u
\(M^*_0\) b -24.2865 1.142 2.6558  
\(M^*_0\) r -23.1925 1.779 1.6683  
\(\phi^*_0\) b 0.0015 2.919 0.0005  
\(\phi^*_0\) r 0.0006 7.691 0.0033 -0.066
\(\alpha\) b -1.2578 0.021    
\(\alpha\) r -0.3091 -0.067    
\(P\) b -0.3020 0.034    
\(P\) r -0.7131 0.233    
\(Q\) b 1.2336 -0.322    
\(Q\) r 1.0689 -0.386    

Additionally, the final table provides the values used to calculate these functional forms, also available in machine-readable form here. The machine-readable .csv file also provides the original, un-corrected literature values of \(M^*_0\) and \(\phi^*_0\) – in linear- and log-form where quoted solely in \(\log_{10}(\phi^*)\) – and \(h\) and \(z_0\) when conversion from non-zero redshift or values in arbitrary \(H_0\) values are quoted.

Citation Band Wavelength / nm Type \(M^*_0\) / AB mag \(\phi^*_0\) / Mpc\(^{-3}\)mag\(^{-1}\) \(\alpha\) Q / mag \(z^{-1}\) P / \(z^{-1}\)
MNRAS 420 1239 u 355.0 b -18.495±0.117 4.493e-03±8.575e-04 -1.430±0.070 5.500±0.600 -7.100±1.500
MNRAS 420 1239 u 355.0 r -17.475±0.157 1.468e-02±4.939e-03 -0.140±0.130 6.400±1.400 -8.100±3.400
MNRAS 420 1239 g 469.0 b -20.045±0.092 2.504e-03±1.029e-04 -1.400±0.030 3.100±0.700 -1.200±1.500
MNRAS 420 1239 g 469.0 r -19.725±0.152 4.322e-03±5.831e-04 -0.430±0.050 3.600±1.400 -3.900±2.800
MNRAS 420 1239 r 617.0 b -20.975±0.067 1.303e-03±1.715e-04 -1.490±0.030 0.800±0.300 2.900±0.600
MNRAS 420 1239 r 617.0 r -20.875±0.032 3.807e-03±5.145e-04 -0.570±0.030 1.800±0.100 -1.200±0.500
MNRAS 420 1239 i 748.0 b -21.285±0.072 1.441e-03±2.058e-04 -1.450±0.020 1.700±0.400 1.200±0.900
MNRAS 420 1239 i 748.0 r -21.205±0.032 3.979e-03±5.145e-04 -0.540±0.030 2.000±0.100 -1.800±0.500
MNRAS 420 1239 z 892.0 b -21.675±0.045 1.166e-03±1.372e-04 -1.450±0.030 0.900±0.200 3.600±0.500
MNRAS 420 1239 z 892.0 r -21.405±0.067 4.528e-03±5.488e-04 -0.490±0.050 2.400±0.300 -2.700±0.700
MNRAS 451 1540 r 617.0 b -21.265±0.051 1.842e-03±2.121e-04 -1.380±0.060 1.090±0.100 1.300±0.250
MNRAS 451 1540 r 617.0 r -21.610±0.063 2.020e-03±2.325e-04 -0.790±0.110 0.580±0.180 1.550±0.400
MNRAS 439 1245 u 355.0 b -18.530±1.250 9.640e-03±1.290e-02 -0.910±7.170    
MNRAS 439 1245 u 355.0 r -18.530±1.250 1.460e-03±9.390e-03 1.250±6.010    
MNRAS 439 1245 g 469.0 b -20.280±0.260 3.510e-03±1.750e-03 -1.290±0.140    
MNRAS 439 1245 g 469.0 r -20.280±0.260 4.880e-03±1.220e-03 0.060±0.590    
MNRAS 439 1245 r 617.0 b -20.900±0.260 4.510e-03±1.030e-03 -1.130±0.070    
MNRAS 439 1245 r 617.0 r -20.900±0.260 3.010e-03±8.300e-04 0.530±0.560    
MNRAS 439 1245 i 748.0 b -21.450±0.200 2.200e-03±1.500e-03 -1.350±0.210    
MNRAS 439 1245 i 748.0 r -21.450±0.200 4.870e-03±1.340e-03 -0.090±0.480    
MNRAS 439 1245 z 892.0 b -21.780±0.250 1.400e-03±1.120e-03 -1.460±0.210    
MNRAS 439 1245 z 892.0 r -21.780±0.250 5.050e-03±8.800e-04 -0.260±0.440    
MNRAS 439 1245 Y 1031.0 b -21.760±0.240 1.440e-03±1.250e-03 -1.450±0.230    
MNRAS 439 1245 Y 1031.0 r -21.760±0.240 4.830e-03±8.400e-04 -0.100±0.540    
MNRAS 439 1245 J 1248.0 b -21.820±0.170 1.580e-03±7.600e-04 -1.380±2.430    
MNRAS 439 1245 J 1248.0 r -21.820±0.170 4.780e-03±7.200e-04 0.080±2.580    
MNRAS 439 1245 H 1631.0 b -22.040±0.260 1.350e-03±6.330e-03 -1.460±2.430    
MNRAS 439 1245 H 1631.0 r -22.040±0.260 5.300e-03±6.690e-03 0.080±2.580    
MNRAS 439 1245 K 2201.0 b -21.720±0.230 1.640e-03±3.130e-03 -1.390±1.620    
MNRAS 439 1245 K 2201.0 r -21.720±0.230 5.090e-03±3.180e-03 0.240±1.550    
ApJ 518 533L U 366.0 b -19.942±0.248 3.259e-03±1.338e-03 -1.140±0.130 0.510±0.660 2.670±0.920
ApJ 518 533L U 366.0 r -19.754±0.264 3.156e-03±8.918e-04 -0.510±0.150 0.970±0.700 0.680±0.690
ApJ 518 533L B 435.0 b -19.981±0.266 2.470e-03±1.132e-03 -1.230±0.120 0.180±0.710 3.080±0.990
ApJ 518 533L B 435.0 r -19.361±0.190 6.963e-03±1.235e-02 0.080±0.140 1.580±0.490 -1.070±0.490
ApJ 518 533L Rc 710.0 b -20.852±0.286 1.921e-03±1.029e-03 -1.340±0.120 0.110±0.740 3.170±1.030
ApJ 518 533L Rc 710.0 r -21.038±0.284 2.744e-03±7.889e-04 -0.630±0.150 0.690±0.760 0.890±0.740
ApJ 697 506 [3.6] 3544.0 b -22.009±0.266 2.573e-03±6.860e-05 -1.400±0.180 1.000±0.700 0.000±0.000
ApJ 697 506 [3.6] 3544.0 r -21.819±0.253 1.509e-03±1.715e-04 -0.630±0.290 1.400±0.500 0.000±0.000
ApJ 697 506 [4.5] 4487.0 b -21.551±0.273 2.470e-03±6.860e-05 -1.290±0.170 0.900±0.700 0.000±0.000
ApJ 697 506 [4.5] 4487.0 r -21.271±0.280 1.269e-03±1.372e-04 -0.600±0.280 1.300±0.500 0.000±0.000
ApJ 697 506 [5.8] 5710.0 b -22.884±0.266 1.406e-03±3.430e-05 -1.630±0.150 0.400±0.700 0.000±0.000
ApJ 697 506 [5.8] 5710.0 r -21.584±0.336 9.947e-04±1.029e-04 -1.330±0.280 1.200±0.800 0.000±0.000
ApJ 697 506 [8.0] 7841.0 b -23.818±0.262 1.509e-03±3.430e-05 -1.350±0.090 1.700±0.800 0.000±0.000
ApJ 697 506 [8.0] 7841.0 r -22.793±1.140 2.401e-04±3.430e-05 -2.030±0.470 1.800±3.500 0.000±0.000
ApJ 560 566 Ks 2159.0 b -21.920±0.060 3.464e-03±4.459e-04 -0.870±0.090    
ApJ 560 566 Ks 2159.0 r -22.470±0.060 1.543e-03±2.058e-04 -0.920±0.100    
MNRAS 427 3244 FUV 152.0 b -17.905±0.045   -1.140±0.015    
MNRAS 427 3244 FUV 152.0 r -16.975±0.200   -0.700±0.195    
MNRAS 427 3244 NUV 227.0 b -18.335±0.040   -1.160±0.015    
MNRAS 427 3244 NUV 227.0 r -17.355±0.140   -0.900±0.115    
MNRAS 427 3244 u 355.0 b -19.465±0.035   -1.140±0.015    
MNRAS 427 3244 u 355.0 r -18.635±0.060   -0.040±0.050    
MNRAS 427 3244 g 469.0 b -20.805±0.035   -1.200±0.025    
MNRAS 427 3244 g 469.0 r -20.275±0.060   -0.070±0.045    
MNRAS 427 3244 r 617.0 b -21.455±0.030   -1.200±0.010    
MNRAS 427 3244 r 617.0 r -21.045±0.065   -0.100±0.045    
MNRAS 427 3244 i 748.0 b -21.935±0.040   -1.280±0.010    
MNRAS 427 3244 i 748.0 r -21.485±0.060   -0.190±0.040    
MNRAS 427 3244 z 892.0 b -22.145±0.035   -1.250±0.010    
MNRAS 427 3244 z 892.0 r -21.715±0.060   -0.170±0.040    
MNRAS 427 3244 Y 1031.0 b -22.315±0.040   -1.250±0.010    
MNRAS 427 3244 Y 1031.0 r -21.875±0.060   -0.250±0.040    
MNRAS 427 3244 J 1248.0 b -22.445±0.040   -1.240±0.015    
MNRAS 427 3244 J 1248.0 r -22.015±0.055   -0.270±0.040    
MNRAS 427 3244 H 1631.0 b -22.695±0.040   -1.210±0.015    
MNRAS 427 3244 H 1631.0 r -22.315±0.055   -0.280±0.035    
MNRAS 427 3244 K 2201.0 b -22.325±0.040   -1.170±0.015    
MNRAS 427 3244 K 2201.0 r -22.035±0.065   -0.310±0.045    
MNRAS 465 672 K 2201.0 b -23.590±0.510 4.270e-04±1.133e-03 -1.516±0.230 0.249±0.340 -0.454±0.880
MNRAS 465 672 K 2201.0 r -23.590±0.510 1.386e-03±1.228e-03 -0.817±0.740 0.249±0.340 -0.725±0.410
A&A 476 137 K 2201.0 b -23.379±0.055 1.195e-03±1.029e-03 -1.300±0.053 0.493±0.044 -0.543±0.073
A&A 476 137 K 2201.0 r -23.161±0.450 1.651e-03±1.102e-03 -0.206±0.610 0.453±0.400 -1.859±0.290
MNRAS 380 585 K 2201.0 b -23.167±0.047 6.637e-04±4.065e-04 -1.232±0.032 0.677±0.039 -0.500±0.074
MNRAS 380 585 K 2201.0 r -22.921±0.034 1.322e-03±6.613e-04 -0.112±0.061 0.416±0.031 -1.049±0.074
IAUS 306 40 r 617.0 b -21.305±0.080 1.334e-03±1.844e-04 -1.470±0.060 0.580±0.050 2.740±0.250
IAUS 306 40 r 617.0 r -21.345±0.070 2.428e-03±2.796e-04 -0.710±0.140 0.790±0.100 1.140±0.250
A&A 508 1217 B 435.0 b -19.961±0.600 4.527e-03±3.120e-03 -1.143±0.360    
A&A 508 1217 B 435.0 r -20.500±0.560 3.634e-03±1.323e-03 -0.618±0.410    
ApJ 647 853 B 435.0 b -20.113±0.015 3.905e-03±3.820e-05 -1.300±0.500 1.232±0.017 -0.456±0.012
ApJ 647 853 B 435.0 r -20.799±0.023 2.220e-03±4.020e-05 -0.500±0.500 0.459±0.027 -0.900±0.026
ApJ 748 10 r 617.0 b -20.919±0.120 3.958e-03±6.339e-04 -1.110±0.500 1.660±0.090 -0.380±0.210
ApJ 748 10 r 617.0 r -21.092±0.070 3.184e-03±4.777e-04 -0.550±0.500 1.730±0.070 -0.950±0.100
ApJ 873 78 K 2201.0 b -22.572±0.023 2.339e-03±2.090e-05 -1.200±0.500 0.601±0.029 -0.652±0.014
ApJ 873 78 K 2201.0 r -22.792±0.019 2.906e-03±5.670e-05 -0.500±0.500 0.192±0.022 -0.459±0.029
ApJ 889 80 IR 504000.0 b -20.774±0.304 9.528e-04±3.281e-04 -0.540±0.241 0.336±0.125 0.046±0.156
ApJ 889 80 IR 504000.0 r -20.774±0.304 6.352e-04±2.187e-04 -0.540±0.241 0.336±0.125 0.046±0.156
MNRAS 494 1894 FUV 154.6 b -18.329±0.120 5.861e-03±1.376e-03 -1.391±0.080 0.886±0.008 -0.405±0.010
MNRAS 494 1894 NUV 234.5 b -18.475±0.090 6.067e-03±1.305e-03 -1.367±0.060 0.975±0.006 -0.419±0.008

Notes

Where applicable, relevant information from each literature reference used to calculate the quoted values in the above table is given below.

Loveday et al. (2012, MNRAS, 420, 1239)

Loveday et al. (2015, MNRAS, 451, 1540)

Kelvin et al. (2014, MNRAS, 439, 1245)

Lin et al. (1999, ApJ, 518, 533)

Dai et al. (2009, ApJ, 697, 506)

Kochanek et al. (2001, ApJ 560 566)

Driver et al. (2012, MNRAS, 427, 3244)

Mortlock et al. (2017, MNRAS, 465, 672)

Arnouts et al. (2007, A&A, 476, 137)

Cirasuolo et al. (2007, MNRAS, 380, 585)

Loveday (2014, IAUS, 306, 40)

Zucca et al. (2009, A&A, 508, 1217)

Willmer et al. (2006, ApJ, 647, 853)

Cool et al. (2012, ApJ, 748, 10)

Beare et al. (2019, ApJ, 873, 78)

Lim et al. (2020, ApJ, 889, 80)

Moutard et al. (2020, MNRAS, 494, 1894)

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