IRSA Queries (astroquery.irsa)¶
Getting started¶
This module can has methods to perform different types of queries on the
catalogs present in the IRSA general catalog service. All queries can be
performed by calling query_region(), with
different keyword arguments. There are 4 different region queries that are
supported: Cone, Box, Polygon and All-Sky. All successful
queries return the results in a Table. We now look at some
examples.
Available catalogs¶
All region queries require a catalog keyword argument, which is the name of
the catalog in the IRSA database, on which the query must be performed. To take
a look at all the available catalogs:
>>> from astroquery.irsa import Irsa
>>> Irsa.list_catalogs()
{'a1763t2': 'Abell 1763 Source Catalog',
'a1763t3': 'Abell 1763 MIPS 70 micron Catalog',
'acs_iphot_sep07': 'COSMOS ACS I-band photometry catalog September 2007',
'akari_fis': 'Akari/FIS Bright Source Catalogue',
'akari_irc': 'Akari/IRC Point Source Catalogue',
'astsight': 'IRAS Minor Planet Survey',
...
...
'xmm_cat_s05': "SWIRE XMM_LSS Region Spring '05 Spitzer Catalog"}
This returns a dictionary of catalog names with their description. If you would rather just print out this information:
>>> from astroquery.irsa import Irsa
>>> Irsa.print_catalogs()
wise_allsky_2band_p1bm_frm WISE Post-Cryo Single Exposure (L1b) Image Inventory Table
wise_allsky_4band_p3as_psr WISE All-Sky Reject Table
cosmos_morph_col_1 COSMOS Zamojski Morphology Catalog v1.0
wise_prelim_p3al_lod WISE Preliminary Release Atlas Inventory Table (Superseded)
com_pccs1_100 Planck PCCS 100GHz Catalog
swire_lhisod SWIRE Lockman Hole ISOCAM Deep Field Catalog
...
...
sdwfs_ch1_epoch3 SDWFS Aug '09 DR1.1 IRAC 3.6um-Selected 3x30sec Coadd, epoch 3 (Feb '08)
Performing a cone search¶
A cone search query is performed by setting the spatial keyword to
Cone. The target name or the coordinates of the search center must also be
specified. The radius for the cone search may also be specified - if this is
missing, it defaults to a value of 10 arcsec. The radius may be specified in
any appropriate unit using a Quantity object. It may also be
entered as a string that is parsable by Angle.
>>> from astroquery.irsa import Irsa
>>> import astropy.units as u
>>> table = Irsa.query_region("m31", catalog="fp_psc", spatial="Cone",
... radius=2 * u.arcmin)
>>> print(table)
ra dec clon clat err_maj ... j_h h_k j_k id
------- ------- ------------ ------------ ------- ... ----- ------ ------ ---
10.685 41.248 00h42m44.45s 41d14m52.56s 0.14 ... 1.792 -0.821 0.971 0
10.697 41.275 00h42m47.39s 41d16m30.25s 0.13 ... -- -- -- 1
10.673 41.254 00h42m41.63s 41d15m15.66s 0.26 ... -- 1.433 -- 2
10.671 41.267 00h42m41.10s 41d15m59.97s 0.17 ... -- -- -- 3
10.684 41.290 00h42m44.11s 41d17m24.99s 0.19 ... 0.261 -1.484 -1.223 4
10.692 41.290 00h42m46.08s 41d17m24.99s 0.18 ... -- -- 0.433 5
10.716 41.260 00h42m51.77s 41d15m36.31s 0.13 ... 0.65 -- -- 6
10.650 41.286 00h42m35.96s 41d17m08.48s 0.41 ... 1.205 -- -- 7
... ... ... ... ... ... ... ... ... ...
10.686 41.271 00h42m44.60s 41d16m14.16s 0.13 ... -- -- -- 768
10.694 41.277 00h42m46.55s 41d16m36.13s 0.27 ... -- -- -- 769
10.690 41.277 00h42m45.71s 41d16m36.54s 0.15 ... -- -- -- 770
10.679 41.281 00h42m42.88s 41d16m51.62s 0.43 ... -- -- -- 771
10.689 41.237 00h42m45.26s 41d14m13.32s 0.22 ... -- -- -- 772
10.661 41.274 00h42m38.53s 41d16m24.76s 0.18 ... -- -- -- 773
10.653 41.281 00h42m36.78s 41d16m52.98s 0.17 ... -- 0.795 -- 774
The coordinates of the center may be specified rather than using the target
name. The coordinates can be specified using the appropriate
astropy.coordinates object. ICRS coordinates may also be entered directly as
a string, as specified by astropy.coordinates:
>>> from astroquery.irsa import Irsa
>>> import astropy.coordinates as coord
>>> table = Irsa.query_region(coord.SkyCoord(121.1743,
... -21.5733, unit=(u.deg,u.deg),
... frame='galactic'),
... catalog='fp_psc', radius='0d2m0s')
>>> print(table)
Performing a box search¶
The box queries have a syntax similar to the cone queries. In this case the
spatial keyword argument must be set to Box. Also the width of the box
region is required. The width may be specified in the same way as the radius
for cone search queries, above - so it may be set using the appropriate
Quantity object or a string parsable by Angle.
>>> from astroquery.irsa import Irsa
>>> import astropy.units as u
>>> table = Irsa.query_region("00h42m44.330s +41d16m07.50s",
... catalog='fp_psc', spatial='Box',
... width=5 * u.arcsec)
WARNING: Coordinate string is being interpreted as an ICRS
coordinate. [astroquery.irsa.core]
>>> print(table)
ra dec clon clat err_maj ... j_h h_k j_k id
------- ------- ------------ ------------ ------- ... ----- ----- ----- ---
10.685 41.269 00h42m44.34s 41d16m08.53s 0.08 ... 0.785 0.193 0.978 0
Note that in this case we directly passed ICRS coordinates as a string to the
query_region().
Queries over a polygon¶
Polygon queries can be performed by setting spatial='Polygon'. The search
center is optional in this case. One additional parameter that must be set for
these queries is polygon. This is a list of coordinate pairs that define a
convex polygon. The coordinates may be specified as usual by using the
appropriate astropy.coordinates object (Again ICRS coordinates may be
directly passed as properly formatted strings). In addition to using a list of
astropy.coordinates objects, one additional convenient means of specifying
the coordinates is also available - Coordinates may also be entered as a list of
tuples, each tuple containing the ra and dec values in degrees. Each of these
options is illustrated below:
>>> from astroquery.irsa import Irsa
>>> from astropy import coordinates
>>> table = Irsa.query_region("m31", catalog="fp_psc", spatial="Polygon",
... polygon=[coordinates.SkyCoord(ra=10.1, dec=10.1, unit=(u.deg, u.deg), frame='icrs'),
... coordinates.SkyCoord(ra=10.0, dec=10.1, unit=(u.deg, u.deg), frame='icrs'),
... coordinates.SkyCoord(ra=10.0, dec=10.0, unit=(u.deg, u.deg), frame='icrs')
... ])
>>> print(table)
ra dec clon clat err_maj ... j_h h_k j_k id
------- ------- ------------ ------------ ------- ... ----- ----- ----- ---
10.016 10.099 00h40m03.77s 10d05m57.22s 0.1 ... 0.602 0.154 0.756 0
10.031 10.063 00h40m07.44s 10d03m47.10s 0.19 ... 0.809 0.291 1.1 1
10.037 10.060 00h40m08.83s 10d03m37.00s 0.11 ... 0.468 0.372 0.84 2
10.060 10.085 00h40m14.39s 10d05m07.60s 0.23 ... 0.697 0.273 0.97 3
10.016 10.038 00h40m03.80s 10d02m17.02s 0.09 ... 0.552 0.313 0.865 4
10.011 10.094 00h40m02.68s 10d05m38.05s 0.23 ... 0.378 0.602 0.98 5
10.006 10.018 00h40m01.33s 10d01m06.24s 0.16 ... 0.662 0.566 1.228 6
Another way to specify the polygon is directly as a list of tuples - each tuple is an ra, dec pair expressed in degrees:
>>> from astroquery.irsa import Irsa
>>> table = Irsa.query_region("m31", catalog="fp_psc", spatial="Polygon",
... polygon = [(10.1, 10.1), (10.0, 10.1), (10.0, 10.0)])
>>> print(table)
ra dec clon clat err_maj ... j_h h_k j_k id
------- ------- ------------ ------------ ------- ... ----- ----- ----- ---
10.016 10.099 00h40m03.77s 10d05m57.22s 0.1 ... 0.602 0.154 0.756 0
10.031 10.063 00h40m07.44s 10d03m47.10s 0.19 ... 0.809 0.291 1.1 1
10.037 10.060 00h40m08.83s 10d03m37.00s 0.11 ... 0.468 0.372 0.84 2
10.060 10.085 00h40m14.39s 10d05m07.60s 0.23 ... 0.697 0.273 0.97 3
10.016 10.038 00h40m03.80s 10d02m17.02s 0.09 ... 0.552 0.313 0.865 4
10.011 10.094 00h40m02.68s 10d05m38.05s 0.23 ... 0.378 0.602 0.98 5
10.006 10.018 00h40m01.33s 10d01m06.24s 0.16 ... 0.662 0.566 1.228 6
Selecting Columns¶
The IRSA service allows to query either a subset of the default columns for a given table, or additional columns that are not present by default. This can be done by listing all the required columns separated by a comma (,) in a string with the selcols argument.
An example where the AllWISE Source Catalog needs to be queried around the star HIP 12 with just the ra, dec and w1mpro columns would be:
>>> from astroquery.irsa import Irsa
>>> table = Irsa.query_region("HIP 12", catalog="allwise_p3as_psd", spatial="Cone", selcols="ra,dec,w1mpro")
>>> print(table)
ra dec clon clat w1mpro dist angle id
deg deg mag arcsec deg
------- ------- ------------ ------------- ------ -------- ---------- ---
0.041 -35.960 00h00m09.79s -35d57m36.94s 4.837 0.350806 245.442148 0
A list of available columns for each catalog can be found at https://irsa.ipac.caltech.edu/holdings/catalogs.html. The “Long Form” button at the top of the column names table must be clicked to access a full list of all available columns.
Changing the precision of ascii output¶
The precision of the table display of each column is set upstream by the archive,
and appears as the .format attribute of individual columns. This attribute affects
not only the display of columns, but also the precision that is output when the table
is written in ascii.ipac or ascii.csv formats. The .format attribute of
individual columns may be set to increase the precision.
>>> from astroquery.irsa import Irsa
>>> table = Irsa.query_region("HIP 12", catalog="allwise_p3as_psd", spatial="Cone", selcols="ra,dec,w1mpro")
>>> table['ra'].format = '{:10.6f}'
>>> table['dec'].format = '{:10.6f}'
>>> print(table)
ra dec clon clat w1mpro dist angle id
deg deg mag arcs deg
----------- ----------- ------------ ------------- ------ -------- ---------- ---
0.0407905 -35.9602605 00h00m09.79s -35d57m36.94s 4.837 0.350806 245.442148 0
Other Configurations¶
By default the maximum number of rows that is fetched is set to 500. However, this option may be changed by changing the astroquery configuration file. To change the setting only for the ongoing python session, you could also do:
>>> from astroquery.irsa import Irsa
>>> Irsa.ROW_LIMIT = 1000 # value of new row limit here.