orchard

A major goal of the IQ Collaboratory is the apples to apples comparison of isolated & quiescent galaxies across observations and simulations. To do so, we have developed Orchard, a framework for creating mock surveys from simulated volumes.

Orchard is currently set up to create SDSS-like surveys from large volume, hydrodynamical simulations. However, the framework is flexible and can be adjusted based on the desired input (semi-analytic models, zoom-in simulations) and output (other surveys such LSST or DESI).

This package is currently intended for IQ internal use. If you are interested in adapting Orchard for your own work, please get in touch with Claire Dickey (http://clairedickey.com).

input

Required inputs	Units	Definition
posvel	Mpc, km/s	Positions (X, Y, Z) and velocities (Vx, Vy, Vz) for each galaxy in the simulation box
mass	M⊙	Total stellar mass for each galaxy
spectra		Synthetic spectra generated for each galaxy
wavelength	Å	Corresponding wavelength array for synthetic spectra
boxsize	Mpc	Simulation box size
little_h		Value of little h used in the simulation
gmag, rmag		SDSS g,r absolute magnitudes derived from the synthetic spectra
d4000		Dn4000 index measured from the synthetic spectra
haew	Å	Ha equivalent width measured from the synthetic spectra
ngals	N	Number of resolved galaxies in the simulation box

Orchard parameters	Units	Definition
dhost_iso_thresh	Mpc	The threshold in projected distance to the nearest potential host galaxy beyond which galaxies are considered isolated
host_mass_thresh	log10(M⊙)	The stellar mass above which galaxies are potential host galaxies for determining isolation
obs_mag_lim	apparent mag	SDSS r band magnitude threshold below which galaxies are not observed in the mock survey
obs_sb_lim	mag / arcsec^2	Surface brightness threshold below which galaxies are not observed in the mock survey
noise_model		Orchard currently has two models for SDSS-like noise; one based on the apparent r magnitude alone, and one based on both r magnitude and g-r color
n_sightlines	N	The number of mock survey sightlines to be generated for the simulation box

output

Outputs	Units	Definition
noisy_spec		Noise-added spectra for all galaxies which are observable in the mock survey
noisy_d4000		Dn4000 measured from the noise-added spectra, used to select quiescent galaxies
noisy_haew	Å	Ha EW measured from the noise-added spectra, used to select quiescent galaxies
dhost_proj	Mpc	Projected distance to the nearest potential host galaxy, used to select isolated galaxies
quiescent_fraction		The quiescent fraction of isolated galaxies measured from the mock survey

example simulation initialization

tng_load_params = {"sim_name":"TNG","plot_color":"#49DF67",
                   ### where the data lives
                   "data_dir":data_dir,
                   "pointers":{
                       "pointer_to_mass":"IQSFSdataTNG-MstarPosVelSat.txt",
                       "pointer_to_posvel":"IQSFSdataTNG-MstarPosVelSat.txt",
                       "pointer_to_specdat":"analyzespectra_TNG_ranincl_medcontflux_sidebands.dat",
                       "pointer_to_spectra":"tng_specs.npy",
                       "pointer_to_specwav":"FSPS_wave_Full.txt"},
                   ### sim params
                   "little_h":0.6774, "boxsize":110.7,
                   ### data column indices
                   "columns":{
                       "mass_col":1, "posvel_col_start":2, 
                       "haew_col":21, "d400_col":19, 
                       "rmag_col":5, "gmag_col":6,},}
                       
run_params = {"dhost_iso_thresh":1.5, ## Mpc thresh for determining isolation
              "host_mass_thresh":10.39, ## log(mass) thresh for determining what's a host gal
              "obs_mag_lim":17.7, ## only galaxies brighter than this get counted
              "obs_sb_lim":23.0, ## only galaxies brighter than this get counted
              "mass_bins":np.arange(8,11.1,0.25), ## stellar mass bins for quiescent fraction measurement
              "noise_model":"sdss_gr_model", ## select noise model
              "n_sightlines":25 ## how many sightlines to run
             }
             
tng = Simulation(run_params,**tng_load_params)
tng.create_multiple_sightlines()

flexibility

Currently, Orchard defines galaxies as quiescent based on Dn4000 and HaEW, and isolated based on projected host distance. Galaxies are selected as observable based on SDSS survey limits, and the noise models are derived from the noise characteristics of SDSS spectroscopy. All of these definitions and limits are easily adjustable, to either use different definitions of quiescence or isolation (e.g., UVJ or distance from the star forming sequence, or central/satellite) or to create synthetic versions of other surveys.