Suntail Hawk (not Pandemonium) will deal 2 damage, because it enters the battlefield as a 2/2.
As Pandemonium states, the creature that enters the battlefield deals the damage.
Whenever a creature enters the battlefield, that creature's controller may have it deal damage equal to its power to any target of their choice.
"It" refers to "that creature".
To answer your actual question: Glorious Anthem is a static ability with a continuous effect:
604.1. Static abilities do something all the time rather than being activated or triggered. They are written as statements, and they’re simply true.
604.2. Static abilities create continuous effects, some of which are prevention effects or replacement effects. These effects are active as long as the permanent with the ability remains on the battlefield and has the ability, or as long as the object with the ability remains in the appropriate zone, as described in rule 113.6.
611.3c Continuous effects that modify characteristics of permanents do so simultaneously with the permanent entering the battlefield. They don’t wait until the permanent is on the battlefield and then change it. Because such effects apply as the permanent enters the battlefield, they are applied before determining whether the permanent will cause an ability to trigger when it enters the battlefield. Example: A permanent with the static ability “All white creatures get +1/+1” is on the battlefield. A creature spell that would normally create a 1/1 white creature instead creates a 2/2 white creature. The creature doesn’t enter the battlefield as 1/1 and then change to 2/2.
All your creatures on the battlefield have +1/+1 as soon as they enter the battlefield. The game never sees a 1/1 Hawk entering the battlefield, it's a 2/2 immediately and will trigger Pandemonium for 2 damage.